Nitride-based semiconductor light-emitting device and method of fabricating the same

ABSTRACT

A nitride-based semiconductor light-emitting device capable of stabilizing transverse light confinement is obtained. This nitride-based semiconductor light-emitting device comprises an emission layer, a cladding layer, formed on the emission layer, including a first nitride-based semiconductor layer and having a current path portion and a current blocking layer, formed to cover the side surfaces of the current path portion, including a second nitride-based semiconductor layer, while the current blocking layer is formed in the vicinity of the current path portion and a region having no current blocking layer is included in a region not in the vicinity of the current path portion. Thus, the width of the current blocking layer is reduced, whereby strain applied to the current blocking layer is relaxed. Consequently, the thickness of the current blocking layer can be increased, thereby stabilizing transverse light confinement.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a nitride-based semiconductorlight-emitting device and a method of fabricating the same, and moreparticularly, it relates to a nitride-based semiconductor light-emittingdevice comprising a current blocking layer and a method of fabricatingthe same.

2. Description of the Background Art

A nitride-based semiconductor laser device, which is one ofnitride-based semiconductor light-emitting devices, is expected as anadvanced light source for a large capacity disk, and subjected to activedevelopment. A well-known general nitride-based semiconductor laserdevice has current blocking layers consisting of a material havingreverse conductivity to a nitride-based semiconductor layer forming aridge portion on side portions of the ridge portion serving as a currentpath portion. This nitride-based semiconductor laser device is disclosedin Japanese Patent Laying-Open No. 10-321962 (1998), for example.

FIG. 69 is a sectional view showing an exemplary structure of aconventional nitride-based semiconductor laser device comprising currentblocking layers 306 having reverse conductivity to a ridge portion.Referring to FIG. 69, an n-type contact layer 302 of n-type GaN isformed on a sapphire substrate 301 in the conventional nitride-basedsemiconductor laser device. An n-type cladding layer 303 of n-type AlGaNand an emission layer 304 of InGaN are formed on the n-type contactlayer 302. A p-type cladding layer 305 of p-type AlGaN having the ridgeportion serving as the current path portion is formed on the emissionlayer 304. The current blocking layers 306 of n-type AlGaN are formed onthe side surfaces of the ridge portion of the p-type cladding layer 305and on flat portions of the p-type cladding layer 305. A p-type contactlayer 307 of p-type GaN is formed on the upper surfaces of the currentblocking layers 306 and the upper surface of the ridge portion of thep-type cladding layer 305. A p-side ohmic electrode 308 is formed on theupper surface of the p-type contact layer 307.

Partial regions of the layers from the p-type cladding layer 305 to then-type contact layer 302 are removed for exposing a surface portion ofthe n-type contact layer 302. An n-side ohmic electrode 309 is formed onthe exposed surface portion of the n-type contact layer 302.

In the conventional nitride-based semiconductor laser device having theaforementioned structure, current flows from the p-side ohmic electrode308 to the emission layer 304, the n-type cladding layer 303, the n-typecontact layer 302 and the n-side ohmic electrode 309 through the p-typecontact layer 307 and the p-type cladding layer 305. Thus, a laser beamcan be emitted from a region of the emission layer 304 located under theridge portion forming the current path portion.

In the aforementioned conventional nitride-based semiconductor laserdevice, the current blocking layers 306 have two functions. First, thecurrent blocking layers 306 are provided on side portions of the currentpath portion, for feeding the current only to the ridge portion formingthe current path portion located substantially at the center of thedevice. Further, the current blocking layers 306 are prepared from amaterial having a refractive index different from that of the p-typecladding layer 305, for confining transverse light in the emission layer304 through the difference between the refractive indices.

In order to strengthen the light confinement in the emission layer 304in this case, the difference between the refractive indices of thep-type cladding layer 305 located on the emission layer 304 and thecurrent blocking layers 306 must be increased. In order to increase thedifference between the refractive indices, the Al composition of thecurrent blocking layers 306 consisting of n-type AlGaN may be increased.In other words, the transverse light can be confined in the emissionlayer 304 by increasing the Al composition of the n-type AlGaN formingthe current blocking layers 306 as compared with the Al composition ofthe p-type AlGaN forming the p-type cladding layer 305. Thenitride-based semiconductor laser device having such a structure isgenerally referred to as a real refractive index guided laser.

In order to confine the transverse light, the current blocking layers306 may alternatively be prepared from a material having a smaller bandgap than the emission layer 304. When an emission layer and currentblocking layers 306 are made of InGaN and the In composition of theInGaN forming the current blocking layers is increased as compared withthat of the InGaN forming the emission layer, for example, the currentblocking layers can absorb part of light generated in the emissionlayer. Thus, transverse light can be confined. The nitride-basedsemiconductor laser device having such a structure is referred to as acomplex refractive index guided laser.

In the aforementioned conventional real refractive index guided laser,the current blocking layers 306 of n-type AlGaN are different in Alcomposition from the p-type cladding layer 305 of p-type AlGaN, andhence the lattice constant of the current blocking layers 306 isdifferent from that of the p-type cladding layer 305. When the Alcomposition of the current blocking layers 306 consisting of n-typeAlGaN is increased, therefore, strain is applied to the current blockinglayers 306 to disadvantageously easily cause cracks or crystal defectssuch as dislocations in the current blocking layers 306. Consequently,it is difficult to form the current blocking layers 306 with a largethickness, leading to difficulty in stabilization of transverse lightconfinement.

In the aforementioned conventional complex refractive index guidedlaser, the current blocking layers of InGaN are prepared from thematerial different from that of the p-type cladding layer consisting ofAlGaN, and hence the lattice constant of the current blocking layers isdifferent from that of the p-type cladding layer. When the Incomposition of the current blocking layers consisting of InGaN isincreased, therefore, strain is applied to the current blocking layersto easily cause lattice defects in the current blocking layers. Also inthis case, it is difficult to form the current blocking layers with alarge thickness, leading to difficulty in stabilization of transverselight confinement.

In the aforementioned nitride-based semiconductor laser device, thecurrent blocking layers 306 are formed above the n-type contact layer302 of GaN formed in a large thickness. In this case, strain isdisadvantageously applied to the current blocking layers 306 due to thedifference between the lattice constants of the current blocking layers306 and the n-type contact layer 302 of GaN having a large thickness.

In the conventional nitride-based semiconductor laser device, further,the ridge portion consisting of the p-type cladding layer 305 is etchedby dry etching or the like for thereafter crystal-growing the currentblocking layers 306. In this case, the p-type cladding layer 305consisting of AlGaN is active and hence a surface portion of the p-typecladding layer 305 exposed by etching is easily contaminated with C orO. Therefore, this contaminant infiltrates into the interfaces betweenthe p-type cladding layer 305 and the current blocking layers 306, todisadvantageously cause crystal defects such as dislocations in thecurrent blocking layers 306.

In the aforementioned conventional real refractive index guided laser,the current blocking layers 306 are formed above a substrate or a thicknitride-based semiconductor layer formed on a substrate. When GaN isemployed as the material for the substrate or the thick nitride-basedsemiconductor layer formed on the substrate and the Al composition ofthe current blocking layers 306 consisting of AlGaN is increased in thiscase, strain is applied to the current blocking layers 306 since thelattice constant of AlGaN forming the current blocking layers 306 issmaller than the lattice constant of GaN. Therefore, cracks or latticedefects are easily caused on the current blocking layers 306.Consequently, it is difficult to thickly form the current blockinglayers 306, disadvantageously leading to difficulty in stabilization oftransverse light confinement.

Also in the aforementioned conventional complex refractive index guidedlaser, the current blocking layers are formed above a substrate or athick nitride-based semiconductor layer formed on a substrate, similarlyto the conventional real refractive index guided laser. When GaN isemployed as the material for the substrate or the thick nitride-basedsemiconductor layer formed on the substrate and the In composition ofthe current blocking layers consisting of InGaN is increased in thiscase, strain is applied to the current blocking layers since the latticeconstant of InGaN forming the current blocking layers is larger than thelattice constant of GaN. Therefore, cracks or lattice defects are easilycaused on the current blocking layers. Also in this case, it isdifficult to thickly form the current blocking layers, disadvantageouslyleading to difficulty in stabilization of transverse light confinement.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a nitride-basedsemiconductor light-emitting device capable of stabilizing transverselight confinement.

Another object of the present invention is to provide a nitride-basedsemiconductor light-emitting device capable of suppressing formation ofcrystal defects resulting from a contaminant on an interface between acladding layer and a current blocking layer.

Still another object of the present invention is to provide a method offabricating a nitride-based semiconductor light-emitting device capableof easily forming a nitride-based semiconductor light-emitting devicecapable of stabilizing transverse light confinement.

In order to attain the aforementioned objects, a nitride-basedsemiconductor light-emitting device according to a first aspect of thepresent invention comprises an emission layer, a cladding layer, formedon the emission layer, including a first nitride-based semiconductorlayer and having a current path portion, and a current blocking layer,formed to cover the side surfaces of the current path portion, includinga second nitride-based semiconductor layer, while the current blockinglayer is formed in the vicinity of the current path portion and a regionnot in the vicinity of the current path portion includes a region havingno current blocking layer. For example, the emission layer may includethe region having no current blocking layer.

The nitride-based semiconductor light-emitting device according to thefirst aspect is so formed that the region not in the vicinity of thecurrent path portion includes the region having no current blockinglayer, whereby the width of the current blocking layer is reduced ascompared with that formed on the overall surface excluding the region inthe vicinity of the current path portion. Thus, strain applied to thecurrent blocking layer due to the difference between the latticeconstants of the current blocking layer and a nitride-basedsemiconductor substrate or a nitride-based semiconductor layer formed ona substrate can be relaxed, whereby the current blocking layer can beinhibited from formation of cracks or lattice defects. Consequently, thethickness of the current blocking layer can be increased, therebystabilizing transverse light confinement.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the first aspect, the current blocking layer is preferablyformed only in the vicinity of the current path portion. According tothis structure, the width of the current blocking layer is reduced,whereby strain applied to the current blocking layer can be furtherrelaxed.

In the aforementioned nitride-based semiconductor light-emitting device,the total width of the current path portion and the current blockinglayer is preferably at least three times and not more than seven timesthe width of the current path portion. If the total width of the currentpath portion and the current blocking layer is smaller than three timesthe width of the current path portion, the range of formation of thecurrent blocking layer is so excessively reduced that transverse lightconfinement is insufficient. If the total width of the current pathportion and the current blocking layer is larger than seven times thewidth of the current path portion, strain applied to the currentblocking layer is so increased as to cause a large number of crystaldefects or cracks on the current blocking layer. Therefore, the totalwidth of the current path portion and the current blocking layer ispreferably at least three times and not more than seven times the widthof the current path portion.

The aforementioned nitride-based semiconductor light-emitting devicepreferably further comprises a mask layer, serving for selectivelygrowing the current blocking layer, formed on the cladding layer at aprescribed space from the current path portion. According to thisstructure, the current blocking layer can be selectively grown by usingthe mask layer, whereby crystallinity of the current blocking layer canbe improved. In this case, the mask layer may be formed at a space of atleast once and not more than three times the width of the current pathportion from the current path portion. According to this structure, thecurrent blocking layer can be selectively grown only in the vicinity ofthe current path portion by using the mask layer serving for a mask ofthe selective growth, whereby strain applied to the current blockinglayer can be easily relaxed. In this case, the mask layer preferablyincludes an oxide film or a nitride film containing at least one elementselected from a group consisting of Si, Ti and Zr.

In the aforementioned nitride-based semiconductor light-emitting device,the cladding layer preferably includes a projection portion forming thecurrent path portion and a flat portion, and the current blocking layeris preferably formed on the side surfaces of the projection portion andon the flat portion. According to this structure, a ridge-typesemiconductor light-emitting device including a current blocking layerinhibited from cracking or the like can be easily, obtained. In thiscase, the mask layer may be formed on the flat portion of the claddinglayer, and the current blocking layer may be formed on the side surfacesof the projection portion of the cladding layer, on the flat portion ofthe cladding layer and on the mask layer.

In the aforementioned nitride-based semiconductor light-emitting device,the current blocking layer preferably includes an opening, and thecladding layer preferably includes a first cladding layer having asubstantially flat upper surface and a second cladding layer, formed onthe first cladding layer in the opening, having the current pathportion. According to this structure, a self-aligned semiconductorlight-emitting device including a current blocking layer inhibited fromcracking or the like can be easily obtained.

A nitride-based semiconductor light-emitting device according to asecond aspect of the present invention comprises an emission layer, acladding layer, formed on the emission layer, including a firstnitride-based semiconductor layer and having a current path portion, anda current blocking layer, formed to cover the side surfaces of thecurrent path portion, including a second nitride-based semiconductorlayer, while a region not in the vicinity of the current path portionincludes a region having the current blocking layer of a thicknesssmaller than the thickness in the vicinity of the current path portion.

In the nitride-based semiconductor light-emitting device according tothe second aspect, the current blocking layer is formed to include theregion having a thickness smaller than the thickness in the vicinity ofthe current path portion in the region not in the vicinity of thecurrent path portion, whereby strain applied to the current blockinglayer due to the difference between the lattice constants of the currentblocking layer and a nitride-based semiconductor substrate or anitride-based semiconductor layer formed on a substrate easilyconcentrates to the region of the current blocking layer having a smallthickness. Thus, crystal defects or cracks are easily formed in theregion, having a small thickness, of the current blocking layer not inthe vicinity of the current path portion, whereby the current blockinglayer can be inhibited from formation of cracks or lattice defects inthe vicinity of the current path portion. Consequently, the thickness ofthe current blocking layer can be increased in the vicinity of thecurrent path portion, thereby stabilizing transverse light confinement.

The aforementioned nitride-based semiconductor light-emitting deviceaccording to the second aspect preferably further comprises a stepportion formed on the region not in the vicinity of the current pathportion, and the region of the current blocking layer having thethickness smaller than the thickness in the vicinity of the current pathportion is preferably formed on the step portion. According to thisstructure, the current blocking layer can be selectively grown on thestep portion, whereby crystallinity of the current blocking layer can beimproved. When the current blocking layer is selectively grown on thestep portion, the region of the current blocking layer having a smallthickness can be easily formed on the step portion. In this case, thestep portion is preferably formed on a position separating from thecurrent path portion by at least once and not more than three times thewidth of the current path portion.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the first or second aspect, the current blocking layerpreferably contains at least one element, selected from a groupconsisting of B, Ga, Al, In and Tl, and N.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the first or second aspect, the current blocking layer ispreferably formed either on a GaN substrate or on a GaN layer formed ona substrate, and preferably includes the second nitride-basedsemiconductor layer having a smaller lattice constant than GaN. In thiscase, strain applied to the current blocking layer due to the differencebetween the lattice constants of the current blocking layer and GaN canbe relaxed, whereby the current blocking layer can be inhibited fromformation of cracks or lattice constants. Consequently, the latticeconstant of the current blocking layer can be reduced or the thicknessthereof can be increased, thereby stabilizing transverse lightconfinement. In this case, the current blocking layer may include anAlGaN layer as the second nitride-based semiconductor layer having asmaller lattice constant than GaN. In this case, the Al composition ofAlGaN can be increased, thereby stabilizing transverse lightconfinement.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the first or second aspect, the current blocking layerpreferably includes the second nitride-based semiconductor layer havinga refractive index smaller than the refractive index of the firstnitride-based semiconductor layer forming the cladding layer. In thiscase, the difference between the refractive indices of the claddinglayer and the current blocking layer can be increased, therebystabilizing transverse light confinement.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the first or second aspect, the current blocking layerpreferably includes the second nitride-based semiconductor layer havinga lattice constant smaller than the lattice constant of the firstnitride-based semiconductor layer forming the cladding layer. In thiscase, the current blocking layer can be inhibited from formation ofcracks or lattice defects. Consequently, the current blocking layer canbe formed with excellent crystallinity. Further, the difference betweenthe lattice constants of the cladding layer and the current blockinglayer can be increased, thereby stabilizing transverse lightconfinement.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the first or second aspect, the current blocking layerpreferably includes an Al_(w)Ga_(1-w)N layer, the cladding layerpreferably includes an Al_(v)Ga_(1-v)N layer, and the current blockinglayer and the cladding layer are preferably formed to have compositionssatisfying w>v. In this case, the current blocking layer can beinhibited from formation of cracks or lattice defects. Consequently, thecurrent blocking layer can be formed with excellent crystallinity.Further, the difference between the Al compositions of the claddinglayer and the current blocking layer can be increased, therebyincreasing the difference between the refractive indices of the claddinglayer and the current blocking layer. Consequently, transverse lightconfinement can be stabilized.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the first or second aspect, the current blocking layer ispreferably formed either on a GaN substrate or on a GaN layer formed ona substrate, and preferably includes the second nitride-basedsemiconductor layer having a lattice constant larger than the latticeconstant of GaN. In this case, strain applied to the current blockinglayer due to the difference between the lattice constants of the currentblocking layer and GaN can be relaxed, whereby the current blockinglayer can be inhibited from formation of lattice defects. Consequently,the current blocking layer can be formed with excellent crystallinity.Further, the lattice constant or the thickness of the current blockinglayer can be increased, thereby stabilizing transverse lightconfinement. In this case, the current blocking layer may contain InGaNfor forming the nitride-based semiconductor layer having the latticeconstant larger than that of GaN. According to this structure, the Incomposition of InGaN can be increased, thereby stabilizing transverselight confinement.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the first or second aspect, the current blocking layerpreferably includes the second nitride-based semiconductor layerabsorbing light emitted from the emission layer. In this case, thecurrent blocking layer can further absorb the light emitted from theemission layer. Consequently, the difference between the refractiveindices of the cladding layer and the current blocking layer can beincreased, thereby stabilizing transverse light confinement. Forexample, the current blocking layer may be formed to include a secondnitride-based semiconductor layer having a smaller band gap than theemission layer.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the first or second aspect, the current blocking layerpreferably includes an In_(s)Ga_(1-s)N layer, the emission layerpreferably includes an In_(x)Ga_(1-x)N layer, and the current blockinglayer and the emission layer are preferably formed to have compositionssatisfying s≧x. In this case, the current blocking layer can beinhibited from formation of lattice defects, whereby the differencebetween the In compositions of the current blocking layer and theemission layer can be increased. Consequently, the current blockinglayer can be formed with excellent crystallinity. Further, the currentblocking layer can further absorb the light emitted from the emissionlayer. Thus, the difference between the refractive indices of thecladding layer and the current blocking layer can be increased, therebystabilizing transverse light confinement.

A nitride-based semiconductor light-emitting device according to a thirdaspect of the present invention comprises an emission layer, a claddinglayer, formed on the emission layer, including a current path portion,and a current blocking layer formed to cover the side surfaces of thecurrent path portion, while the current blocking layer includes adielectric blocking layer and a semiconductor blocking layer formed onthe dielectric blocking layer.

In the nitride-based semiconductor light-emitting device according tothe third aspect, the current blocking layer is formed to include thedielectric blocking layer and the semiconductor blocking layer formed onthe dielectric blocking layer as hereinabove described, whereby thedielectric blocking layer can be interposed between the cladding layerand the semiconductor blocking layer. Thus, the cladding layer and thesemiconductor blocking layer can be inhibited from coming into contactwith each other. Therefore, strain applied to the semiconductor blockinglayer due to the difference between the lattice constants of thecladding layer and the semiconductor blocking layer can be relaxed,whereby the semiconductor blocking layer can be inhibited from formationof cracks or crystal defects such as dislocations. Further, the claddinglayer and the semiconductor blocking layer can be inhibited from cominginto contact with each other, thereby preventing formation of crystaldefects resulting from a contaminant on the interface between thecladding layer and the semiconductor blocking layer. In addition, thedielectric blocking layer can be interposed between the semiconductorblocking layer and the underlayer, thereby relaxing strain applied tothe semiconductor blocking layer due to the difference between thelattice constants of the semiconductor blocking layer and the underlayerformed by a thick nitride-based semiconductor layer such as a GaN layer,for example. The semiconductor blocking layer can be inhibited fromformation of cracks or crystal defects such as dislocations also in thiscase.

According to the third aspect, the semiconductor blocking layer can beinhibited from formation of cracks or crystal defects as hereinabovedescribed, whereby the thickness of the current blocking layer can beincreased for obtaining a nitride-based semiconductor light-emittingdevice capable of stabilizing transverse light confinement as a result.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the third aspect, the dielectric blocking layer preferablyincludes an opening reaching the upper surface of the cladding layer,and the semiconductor blocking layer is preferably in contact with theupper surface of the cladding layer through the opening of thedielectric blocking layer. According to this structure, the contact areabetween the cladding layer and the semiconductor blocking layer can bereduced, thereby inhibiting formation of crystal defects such asdislocations or cracks resulting from the difference between the latticeconstants of the cladding layer and the semiconductor blocking layer orformation of crystal defects resulting from a contaminant on theinterface between the cladding layer and the semiconductor blockinglayer.

In this case, the semiconductor blocking layer is preferably formed byselective growth from the upper surface of the cladding layer located inthe opening of the dielectric blocking layer. According to thisstructure, the semiconductor blocking layer having excellentcrystallinity can be easily formed on the cladding layer.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the third aspect, the thickness of the dielectric blockinglayer is preferably smaller than the thickness of the semiconductorblocking layer. According to this structure, the semiconductor blockinglayer having higher thermal conductivity than the dielectric blockinglayer can effectively radiate heat generated in the emission layer.Consequently, excellent characteristics can be obtained also inhigh-temperature operation or high-output operation of the nitride-basedsemiconductor light-emitting device.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the third aspect, the cladding layer preferably includes aprojection portion forming the current path portion and a flat portion,and the current blocking layer is preferably formed on the side surfacesof the projection portion and on the flat portion. According to thisstructure, a ridge-type nitride-based semiconductor light-emittingdevice including the current blocking layer inhibited from formation ofcrystal defects or cracks can be easily obtained.

In this case, the dielectric blocking layer is preferably formed on theflat portion of the cladding layer, and the semiconductor blocking layeris preferably formed on the side surfaces of the projection portion ofthe cladding layer and on the dielectric blocking layer formed on theflat portion. According to this structure, the cladding layer and thesemiconductor blocking layer come into contact with each other only onthe side surfaces of the projection portion of the cladding layer,whereby the contact area between the cladding layer and thesemiconductor blocking layer can be reduced. In this case, thesemiconductor blocking layer is preferably formed by selective growthfrom the side surfaces of the projection portion of the cladding layer.According to this structure, the semiconductor blocking layer can beeasily formed with excellent crystallinity.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the third aspect, the current blocking layer preferablyincludes an opening, and the cladding layer preferably includes a firstcladding layer having a substantially flat upper surface and a secondcladding layer, formed on the first cladding layer in the opening of thecurrent blocking layer, having the current path portion. According tothis structure, a self-aligned nitride-based semiconductorlight-emitting device including a current blocking layer inhibited fromformation of crystal defects or cracks can be easily obtained.

In this case, the second cladding layer is preferably formed to extendonto the upper surface of the current blocking layer. According to thisstructure, the area of the upper surface of the second cladding layer isso increased that contact resistance between the second cladding layerand the contact layer formed thereon can be reduced.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the third aspect, the number of vertical dislocations ispreferably reduced in the semiconductor blocking layer due totransversely bent dislocations. According to this structure, thesemiconductor blocking layer can be obtained with more excellentcrystallinity.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the third aspect, the semiconductor blocking layer ispreferably formed only in the vicinity of the current path portion.According to this structure, the width of the semiconductor blockinglayer is so reduced that strain applied to the semiconductor blockinglayer due to the difference between the lattice constants of thecladding layer and the semiconductor blocking layer can be furtherrelaxed. Thus, the semiconductor blocking layer can be inhibited fromformation of cracks or crystal defects. Consequently, the thickness ofthe semiconductor blocking layer can be increased, thereby stabilizingtransverse light confinement. Further, the semiconductor blocking layeris so formed only in the vicinity of the current path portion as toreduce the capacitance between the current blocking layer including thesemiconductor blocking layer and the dielectric blocking layer and thecladding layer. Thus, a pulse for operating the device can quickly riseand fall, whereby a nitride-based semiconductor laser device allowinghigh-speed pulsed operation can be obtained.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the third aspect, the semiconductor blocking layerpreferably contains at least one element, selected from a groupconsisting of B, Ga, Al, In and Tl, and N. According to this structure,the semiconductor blocking layer can be formed with excellentcrystallinity.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the third aspect, the cladding layer preferably includes afirst nitride-based semiconductor layer, and the semiconductor blockinglayer is preferably formed either on a GaN substrate or on a GaN layerformed on a substrate, and preferably includes a second nitride-basedsemiconductor layer having a smaller lattice constant than GaN. In thiscase, strain applied to the semiconductor blocking layer due to thedifference between the lattice constants of the semiconductor blockinglayer and GaN can be relaxed, thereby inhibiting the semiconductorblocking layer from formation of cracks or lattice defects.Consequently, the lattice constant of the semiconductor blocking layercan be reduced or the thickness thereof can be increased, therebystabilizing transverse light confinement. In this case, thesemiconductor blocking layer may include an AlGaN layer as the secondnitride-based semiconductor layer having a lattice constant smaller thanthat of GaN. In this case, the Al composition of the AlGaN layer can beincreased, thereby stabilizing transverse light confinement.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the third aspect, the cladding layer preferably includes afirst nitride-based semiconductor layer, and the semiconductor blockinglayer preferably includes a second nitride-based semiconductor layerhaving a refractive index smaller than the refractive index of the firstnitride-based semiconductor layer forming the cladding layer. In thiscase, the difference between the refractive indices of the claddinglayer and the semiconductor blocking layer can be increased, therebystabilizing transverse light confinement.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the third aspect, the cladding layer preferably includes afirst nitride-based semiconductor layer, and the semiconductor blockinglayer preferably includes a second nitride-based semiconductor layerhaving a lattice constant smaller than the lattice constant of the firstnitride-based semiconductor layer forming the cladding layer. In thiscase, the semiconductor blocking layer can be inhibited from formationof cracks or lattice defects, whereby the semiconductor blocking layercan be formed with excellent crystallinity. Further, the differencebetween the lattice constants of the cladding layer and thesemiconductor blocking layer can be increased, thereby stabilizingtransverse light confinement.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the third aspect, the current blocking layer preferablyincludes an Al_(w)Ga_(1-w)N layer, the cladding layer preferablyincludes an Al_(v)Ga_(1-v)N layer, and the current blocking layer andthe cladding layer are preferably formed to have compositions satisfyingw>v. In this case, the semiconductor blocking layer can be inhibitedfrom formation of cracks or lattice defects, whereby the semiconductorblocking layer can be formed with excellent crystallinity. Further, thedifference between the Al compositions of the cladding layer and thesemiconductor blocking layer can be increased, thereby increasing thedifference between the refractive indices of the cladding layer and thesemiconductor blocking layer. Consequently, transverse light confinementcan be stabilized.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the third aspect, the cladding layer preferably includes afirst nitride-based semiconductor layer, and the semiconductor blockinglayer preferably is preferably formed either on a GaN substrate or on aGaN layer formed on a substrate, and preferably includes a secondnitride-based semiconductor layer having a lattice constant larger thanthe lattice constant of GaN. In this case, strain applied to thesemiconductor blocking layer due to the difference between the latticeconstants of the semiconductor blocking layer and GaN can be relaxed,thereby inhibiting the semiconductor blocking layer from formation oflattice defects. Consequently, the semiconductor blocking layer can beformed with excellent crystallinity. Further, the lattice constant orthe thickness of the semiconductor blocking layer can be increased,thereby stabilizing transverse light confinement. In this case, thesemiconductor blocking layer may be formed to contain InGaN forming thenitride-based semiconductor layer having the larger lattice constantthan GaN. In this case, the In composition of InGaN can be increased,thereby stabilizing transverse light confinement.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the third aspect, the cladding layer preferably includes afirst nitride-based semiconductor layer, and the semiconductor blockinglayer preferably includes a second nitride-based semiconductor layerabsorbing light emitted from the emission layer. According to thisstructure, the semiconductor blocking layer can further absorb the lightemitted from the emission layer. Consequently, the difference betweenthe refractive indices of the cladding layer and the semiconductorblocking layer can be increased, thereby stabilizing transverse lightconfinement. For example, the semiconductor blocking layer may be formedto include the second nitride-based semiconductor layer having a smallerband gap than the emission layer.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the third aspect, the semiconductor blocking layerpreferably includes an In_(s)Ga_(1-s)N layer, the emission layerpreferably includes an In_(s)Ga_(1-x)N layer, and the semiconductorblocking layer and the emission layer are preferably formed to havecompositions satisfying s≧x. According to this structure, thesemiconductor blocking layer can be inhibited from formation of latticedefects, whereby the difference between the In compositions of thesemiconductor blocking layer and the emission layer can be increased.Consequently, the semiconductor blocking layer can be formed withexcellent crystallinity. Further, the semiconductor blocking layer canfurther absorb the light emitted from the emission layer. Thus, thedifference between the refractive indices of the cladding layer and thesemiconductor blocking layer can be increased, thereby stabilizingtransverse light confinement.

In the aforementioned nitride-based semiconductor light-emitting deviceaccording to the third aspect, the dielectric blocking layer preferablyincludes an oxide film or a nitride film containing at least one elementselected from a group consisting of Si, Ti and Zr. According to thisstructure, the dielectric blocking layer can easily relax the differencebetween the lattice constants of the cladding layer or a thicknitride-based semiconductor layer forming the underlayer and thesemiconductor blocking layer. In this case, the dielectric blockinglayer may include an SiN film.

A method of fabricating a nitride-based semiconductor light-emittingdevice according to a fourth aspect of the present invention comprisessteps of forming a cladding layer including a first nitride-basedsemiconductor layer and having a current path portion on an emissionlayer, and forming a current blocking layer including a secondnitride-based semiconductor layer in the vicinity of the current pathportion to cover the side surfaces of the current path portion whileforming a region having no current blocking layer on a region not in thevicinity of the current path portion.

In the method of fabricating a nitride-based semiconductorlight-emitting device according to the fourth aspect, the region havingno current blocking layer is formed on the region not in the vicinity ofthe current path portion as hereinabove described, whereby the width ofthe current blocking layer is reduced as compared with that formed onthe overall surface excluding the region in the vicinity of the currentpath portion. Thus, strain applied to the current blocking layer due tothe difference between the lattice constants of the current blockinglayer and a nitride-based semiconductor substrate or a nitride-basedsemiconductor layer formed on a substrate can be relaxed, whereby thecurrent blocking layer can be inhibited from formation of cracks orlattice defects. Consequently, the thickness of the current blockinglayer can be increased, thereby easily forming a nitride-basedsemiconductor light-emitting device capable of stabilizing transverselight confinement.

The aforementioned method of fabricating a nitride-based semiconductorlight-emitting device according to the fourth aspect preferably furthercomprises a step of forming a mask layer on the cladding layer at aprescribed space from the current path portion, and the step of formingthe current blocking layer preferably includes a step of forming thecurrent blocking layer only in the vicinity of the current path portionto cover the side surfaces of the current path portion by selectivelygrowing the current blocking layer by using the mask layer. According tothis structure, the current blocking layer can be selectively grown byusing the mask layer, whereby crystallinity of the current blockinglayer can be improved. Further, the current blocking layer can beselectively grown only in the vicinity of the current path portion byusing the mask layer serving as a mask, whereby strain applied to thecurrent blocking layer can be easily relaxed.

A method of fabricating a nitride-based semiconductor light-emittingdevice according to a fifth aspect of the present invention comprisessteps of forming a cladding layer including a first nitride-basedsemiconductor layer and having a current path portion on an emissionlayer, and forming a current blocking layer, covering the side surfacesof the current path portion, including a second nitride-basedsemiconductor layer, having a region of a thickness smaller than thethickness in the vicinity of the current path portion on a region not inthe vicinity of the current path portion.

In the method of fabricating a nitride-based semiconductorlight-emitting device according to the fifth aspect, the currentblocking layer is formed on the region not in the vicinity of thecurrent path portion to include the region having a thickness smallerthan the thickness in the vicinity of the current path portion, wherebystrain applied to the current blocking layer due to the differencebetween the lattice constants of the current blocking layer and anitride-based semiconductor substrate or a nitride-based semiconductorlayer formed on a substrate easily concentrates to the region of thecurrent blocking layer having a small thickness. Thus, crystal defectsor cracks are easily formed in the region, having a small thickness, ofthe current blocking layer not in the vicinity of the current pathportion, whereby the current blocking layer can be inhibited fromformation of cracks or lattice defects in the vicinity of the currentpath portion. Consequently, the thickness of the current blocking layercan be increased in the vicinity of the current path portion, whereby anitride-based semiconductor light-emitting device capable of stabilizingtransverse light confinement can be easily formed.

In the aforementioned method of fabricating a nitride-basedsemiconductor light-emitting device according to the fifth aspect, thestep of forming the current blocking layer preferably includes steps offorming a step portion on the region not in the vicinity of the currentpath portion and selectively growing the current blocking layer in thevicinity of the current path portion on the step portion thereby formingthe region of the current blocking layer having the thickness smallerthan the thickness of the current blocking layer in the vicinity of thecurrent path portion on the step portion. According to this structure,the current blocking layer can be selectively grown on the step portion,whereby crystallinity of the current blocking layer can be improved.When the current blocking layer is selectively grown on the stepportion, the region of the current blocking layer having a smallthickness can be easily formed on the step portion.

A method of fabricating a nitride-based semiconductor light-emittingdevice according to a sixth aspect of the present invention comprisessteps of forming a first cladding layer including a first nitride-basedsemiconductor layer on an emission layer, forming a current blockinglayer, including a second nitride-based semiconductor layer, having anopening in the vicinity of a region formed with a current path portion,and forming a second cladding layer, including a third nitride-basedsemiconductor layer, forming the current path portion on the firstcladding layer in the opening of the current blocking layer.

In the method of fabricating a nitride-based semiconductorlight-emitting device according to the sixth aspect, the currentblocking layer including the second nitride-based semiconductor layerhaving the opening is formed in the vicinity of the region formed withthe current path portion and thereafter the second cladding layerincluding the third nitride-based semiconductor layer forming thecurrent path portion is formed on the first cladding layer in theopening of the current blocking layer as hereinabove described, therebyeasily forming a self-aligned nitride-based semiconductor light-emittingdevice having the current blocking layer formed only in the vicinity ofthe current path portion. Thus, the width of the current blocking layeris reduced as compared with that formed on the overall surface excludingthe region in the vicinity of the current path portion. Therefore,strain applied to the current blocking layer due to the differencebetween the lattice constants of the current blocking layer and anitride-based semiconductor substrate or a nitride-based semiconductorlayer formed on a substrate can be relaxed, thereby inhibiting thecurrent blocking layer from formation of cracks or lattice defects.Consequently, the thickness of the current blocking layer can beincreased, thereby easily forming a self-aligned nitride-basedsemiconductor light-emitting device capable of stabilizing transverselight confinement.

The aforementioned method of fabricating a nitride-based semiconductorlight-emitting device according to the sixth aspect preferably furthercomprises a step of forming a mask layer on the first cladding layer ata prescribed space from the region formed with the current path portion,and the step of forming the current blocking layer preferably includes astep of selectively growing the current blocking layer by using the masklayer thereby forming the current blocking layer only in the vicinity ofthe region formed with the current path portion. According to thisstructure, the current blocking layer can be selectively grown by usingthe mask layer, whereby crystallinity of the current blocking layer canbe improved in the self-aligned nitride-based semiconductorlight-emitting device. Further, the current blocking layer can beselectively grown only in the vicinity of the current path portion byusing the mask layer serving for a mask of the selective growth, wherebystrain applied to the current blocking layer can be easily relaxed inthe self-aligned nitride-based semiconductor light-emitting device.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a nitride-based semiconductor laserdevice according to a first embodiment of the present invention;

FIGS. 2 to 7 are sectional views for illustrating a method offabricating the nitride-based semiconductor laser device according tothe first embodiment of the present invention;

FIG. 8 is a sectional view showing a nitride-based semiconductor laserdevice according to a second embodiment of the present invention;

FIGS. 9 to 14 are sectional views for illustrating a method offabricating the nitride-based semiconductor laser device according tothe second embodiment of the present invention;

FIG. 15 is a sectional view showing a nitride-based semiconductor laserdevice according to a third embodiment of the present invention;

FIGS. 16 to 19 are sectional views for illustrating a method offabricating the nitride-based semiconductor laser device according tothe third embodiment of the present invention;

FIG. 20 is a sectional view showing a nitride-based semiconductor laserdevice according to a fourth embodiment of the present invention;

FIGS. 21 to 24 are sectional views for illustrating a method offabricating the nitride-based semiconductor laser device according tothe fourth embodiment of the present invention;

FIG. 25 is a perspective view showing a nitride-based semiconductorlaser device according to a fifth embodiment of the present invention;

FIGS. 26 to 32 are sectional views for illustrating a method offabricating the nitride-based semiconductor laser device according tothe fifth embodiment of the present invention;

FIG. 33 is a perspective view showing a nitride-based semiconductorlaser device according to a modification of the fifth embodiment of thepresent invention;

FIG. 34 is a perspective view showing a nitride-based semiconductorlaser device according to a sixth embodiment of the present invention;

FIGS. 35 to 37 are sectional views for illustrating a method offabricating the nitride-based semiconductor laser device according tothe sixth embodiment of the present invention;

FIG. 38 is a perspective view showing a nitride-based semiconductorlaser device according to a modification of the sixth embodiment of thepresent invention;

FIG. 39 is a perspective view showing a nitride-based semiconductorlaser device according to a seventh embodiment of the present invention;

FIGS. 40 to 45 are sectional views for illustrating a method offabricating the nitride-based semiconductor laser device according tothe seventh embodiment of the present invention;

FIG. 46 is a perspective view showing a nitride-based semiconductorlaser device according to a modification of the seventh embodiment ofthe present invention;

FIG. 47 is a perspective view showing a nitride-based semiconductorlaser device according to an eighth embodiment of the present invention;

FIGS. 48 to 51 are sectional views for illustrating a method offabricating the nitride-based semiconductor laser device according tothe eighth embodiment of the present invention;

FIG. 52 is a perspective view showing a nitride-based semiconductorlaser device according to a modification of the eighth embodiment of thepresent invention;

FIG. 53 is a perspective view showing a nitride-based semiconductorlaser device according to a ninth embodiment of the present invention;

FIGS. 54 to 56 are sectional views for illustrating a method offabricating the nitride-based semiconductor laser device according tothe ninth embodiment of the present invention;

FIG. 57 is a perspective view showing a nitride-based semiconductorlaser device according to a modification of the ninth embodiment of thepresent invention;

FIG. 58 is a perspective view showing a nitride-based semiconductorlaser device according to a tenth embodiment of the present invention;

FIGS. 59 and 60 are sectional views for illustrating a method offabricating the nitride-based semiconductor laser device according tothe tenth embodiment of the present invention;

FIG. 61 is a perspective view showing a nitride-based semiconductorlaser device according to a modification of the tenth embodiment of thepresent invention;

FIG. 62 is a perspective view showing a nitride-based semiconductorlaser device according to an eleventh embodiment of the presentinvention;

FIGS. 63 to 67 are sectional views for illustrating a method offabricating the nitride-based semiconductor laser device according tothe eleventh embodiment of the present invention;

FIG. 68 is a perspective view showing a nitride-based semiconductorlaser device according to a modification of the eleventh embodiment ofthe present invention; and

FIG. 69 is a sectional view showing a conventional nitride-basedsemiconductor laser device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are now described with reference tothe drawings.

(First Embodiment)

The structure of a nitride-based semiconductor laser device according toa first embodiment of the present invention is described with referenceto FIG. 1. This nitride-based semiconductor laser device according tothe first embodiment is a complex refractive index guided laser device.

In the structure of the nitride-based semiconductor laser deviceaccording to the first embodiment, a buffer layer 2 of AlGaN having athickness of about 15 nm and an undoped GaN layer 3 having a thicknessof about 0.5 μm are formed on a sapphire (0001) plane substrate 1(hereinafter referred to as “sapphire substrate 1”). An n-type contactlayer 4, having a mesa portion of about 70 μm in width, consisting ofn-type GaN having a thickness of about 4 μm is formed on the undoped GaNlayer 3. The sapphire substrate 1 is an example of the “substrate”according to the present invention, and the n-type contact layer 4 is anexample of the “nitride-based semiconductor layer” according to thepresent invention.

An anti-cracking layer 5 of n-type In_(0.05)Ga_(0.95)N having athickness of about 0.1 μm, an n-type second cladding layer 6 of Si-dopedAl_(0.3)Ga_(0.7)N having a thickness of about 1 μm, an n-type firstcladding layer 7 of Si-doped GaN having a thickness of about 50 nm and amultiple quantum well (MQW) emission layer 8 consisting of an MQW ofInGaN are formed on the upper surface of the mesa portion of the n-typecontact layer 4. The MQW emission layer 8 is formed by alternatelystacking five barrier layers of undoped In_(y)Ga_(1-y)N (In composition:y=0, i.e., GaN) each having a thickness of about 4 nm and four welllayers of undoped In_(x)Ga_(1-x)N (In composition: x=0.15) each having athickness of about 4 nm. The MQW emission layer 8 is an example of the“emission layer” according to the present invention.

A p-type first cladding layer 9 of Mg-doped GaN having a thickness ofabout 40 nm is formed on the MQW emission layer 8. A p-type secondcladding layer 10 of Mg-doped Al_(v)Ga_(1-v)N (Al composition: v=0.08)having a width of about 2 μm and a thickness of about 0.45 μm is formedon the upper surface of the p-type first cladding layer 9. A cap layer11 of p-type GaN having a thickness of about 50 nm is formed to besubstantially in contact with the overall upper surface of the p-typesecond cladding layer 10. The p-type second cladding layer 10 and thecap layer 11 form a current path portion (ridge portion) 12 having awidth W1 (about 2 μm in the first embodiment). The p-type first claddinglayer 9 and the p-type second cladding layer 10 are examples of the“cladding layer” according to the present invention.

A mask layer 13 of a silicon nitride such as Si₃N₄ having an opening ofabout 10 μm in width around the current path portion 12 is formed on theupper surface of the p-type first cladding layer 9. A current blockinglayer 14 of Si-doped In_(s)Ga_(1-s)N (In composition:s=0.2) having athickness of about 3 μm is formed on the upper surface of the p-typefirst cladding layer 9 exposed in the opening of the mask layer 13 andon a partial region of the upper surface of the mask layer 13, to fillup side portions of the current path portion 12. In this case, the totalwidth W2 (about 10 μm) of the current path portion 12 and the currentblocking layer 14 is set in the range of at least three times and notmore than seven times (five times in the first embodiment) the width W1(about 2 μm) of the current path portion 12, for the following reason:

If the total width W2 of the current path portion 12 and the currentblocking layer 14 is smaller than three times the width W1 of thecurrent path portion 12, the range of formation of the current blockinglayer 14 is so excessively reduced that transverse light confinement isinsufficient. If the total width W2 of the current path portion 12 andthe current blocking layer 14 is larger than seven times the width W1 ofthe current path portion 12, strain applied to the current blockinglayer 14 is increased to result in a large number of lattice defects inthe current blocking layer 14. Therefore, the total width W2 of thecurrent path portion 12 and the current blocking layer 14 is preferablyset in the range of at least three times and not more than seven timesthe width W1 of the current path portion 12.

A p-type contact layer 15 of Mg-doped GaN having a thickness of about 3μm to about 5 μm is formed on the current path portion 12 and on thecurrent blocking layer 14 to substantially cover the overall uppersurface of the current path portion 12 (the cap layer 11) and a partialregion of the upper surface of the current blocking layer 14. Each ofthe layers 2 to 11, 14 and 15 has a wurtzite structure, and is formed bygrowing in the [0001] direction of the nitride-based semiconductor.

A p-side electrode 16 of Au/Pd is formed on the p-type contact layer 15by stacking Pd and Au layers on the p-type contact layer 15 in thisorder. An n-side electrode 17 of Au/Ti is formed on the exposed surfaceportion of the n-type contact layer 4 by stacking Ti and Au layers onthe n-type contact layer 4 in this order.

According to the first embodiment, the current blocking layer 14 isformed in the range of the width W2 (about 10 μm) of the opening of themask layer 13 as hereinabove described, so that the current blockinglayer 14 can be formed only in the vicinity of the current path portion12. Therefore, the width of the current blocking layer 14 is reduced ascompared with that formed on the overall surface, which consists of thevicinity of the current path portion 12 and the region excluding thevicinity of the current path portion 12. Thus, strain applied to thecurrent blocking layer 14 due to the difference between the latticeconstants of the current blocking layer 14 and the n-type contact layer4 of n-type GaN formed on the sapphire substrate 1 with the largethickness of about 4 μm can be relaxed, thereby inhibiting the currentblocking layer 14 from formation of lattice defects. Consequently, thethickness of the current blocking layer 14 can be increased, therebystabilizing transverse light confinement.

A method of fabricating the nitride-based semiconductor laser deviceaccording to the first embodiment is now described with reference toFIGS. 1 to 7.

First, the buffer layer 2 of AlGaN having the thickness of about 15 nmis formed on the sapphire substrate 1 by MOVPE (metal organic vaporphase epitaxy) under the atmospheric pressure while holding thesubstrate temperature at about 600° C., as shown in FIG. 2. Then, theundoped GaN layer 3 having the thickness of about 0.5 μm and the n-typecontact layer 4 of Si-doped GaN having the thickness of about 4 μm areformed on the buffer layer 2 while holding the substrate temperature atabout 1150° C. Further, the anti-cracking layer 5 of n-typeIn_(0.05)Ga_(0.95)N having the thickness of about 0.1 μm is formed onthe n-type contact layer 4 while holding the substrate temperature atabout 880° C. The n-type second cladding layer 6 of Si-dopedAl_(0.3)Ga_(0.7)N having the thickness of about 1 μm and the n-typefirst cladding layer 7 of Si-doped GaN having the thickness of about 50nm are formed on the anti-cracking layer 5 while holding the substratetemperature at about 1150° C.

Then, five undoped GaN barrier layers and four undopedIn_(0.15)Ga_(0.85)N well layers are alternately stacked on the n-typefirst cladding layer 7 while holding the substrate temperature at about880° C., thereby forming the MQW emission layer 8. The p-type firstcladding layer 9 of Mg-doped GaN having the thickness of about 40 nm,the p-type second cladding layer 10 of Mg-doped AlGaN (Al composition:0.08) having the thickness of about 0.45 μm and the cap layer 11 ofp-type GaN having the thickness of about 50 nm are successively formedon the MQW emission layer 8 while holding the substrate temperature atabout 1150° C.

Thereafter a striped Ni mask layer 18 having a width of about 2 μm isformed on a prescribed region of the cap layer 11, as shown in FIG. 3.This Ni mask layer 18 is employed as a mask for etching the cap layer 11and the p-type second cladding layer 10 to partially expose the p-typefirst cladding layer 9 by RIE (reactive ion etching) or the like withetching gas of CF₄, for example. Thus, the current path portion (ridgeportion) 12 is formed by the p-type second cladding layer 10 having thewidth of about 2 μm and the cap layer 11 as show in FIG. 3. Thereafterthe Ni mask layer 18 is removed.

Then, a silicon nitride layer (not shown) of Si₃N₄ or the like is formedto cover the overall surface by ECR (electron cyclotron resonance)plasma CVD (chemical vapor deposition), for example, and thereafterpatterned by photolithography and wet etching employing BHF (bufferedhydrofluoric acid) thereby forming the mask layer 13 as shown in FIG. 4.This mask layer 13 is formed on the upper surface of the current pathportion 12 (the cap layer 11) and on partial regions of the uppersurface of the p-type first cladding layer 9. The mask layer 13 isformed to have the opening of about 10 μm in width around the currentpath portion 12 on the upper surface of the p-type first cladding layer9. The upper surface of the p-type first cladding layer 9 is partiallyexposed in the opening of the mask layer 13.

Then, the mask layer 13 is employed as a mask for selectively growingthe current blocking layer 14 having the thickness of about 3 μm on theexposed part of the upper surface of the p-type first cladding layer 9by low-pressure MOVPE with pressure of about 1×10⁴ Pa to cover the sideportions of the current path portion 12, as shown in FIG. 5. In thiscase, the flow rate of NH₃ is set to about three times that of NH₃employed for MOVPE under the atmospheric pressure while holding thesubstrate temperature at about 880° C., for example. The currentblocking layer 14 grown under such conditions is formed on the part ofthe upper surface of the p-type first cladding layer 9 exposed in theopening of the mask layer 13 and on partial regions of the upper surfaceof the mask layer 13 to cover the side portions of the current pathportion 12. Thereafter the mask layer 13 is removed from the currentpath portion 12 (the cap layer 11).

Then, the p-type contact layer 15 of Mg-doped GaN having the thicknessof about 3 μm to about 5 μm is formed on the current path portion 12(the cap layer 11) and on the current blocking layer 14 by low-pressureMOVPE with pressure of about 1×10⁴ Pa, as shown in FIG. 6. In this case,Mg-doped GaN is selectively grown on the current path portion 12 (thecap layer 11) and on the current blocking layer 14. Thus, the p-typecontact layer 15 having the width of about 8 μm is formed around thecurrent path portion 12. Raw material gas for forming the layers 2 to11, 14 and 15 consisting of nitride semiconductors on the sapphiresubstrate 1 by MOVPE is prepared from trimethyl aluminum (TMAl),trimethyl gallium (TMGa), trimethyl indium (TMIn), NH₃, SiH₄ orcyclopentadienyl magnesium (Cp₂Mg), for example.

Then, a striped Ni mask (not shown) having a width of about 70 μm and athickness of about 3 μm to about 5 μm, for example, is formed on aprescribed region of the wafer through a metal mask by EB (electronbeam) deposition. Thereafter partial regions of the mask layer 13, thep-type first cladding layer 9, the MQW emission layer 8, the n-typefirst cladding layer 7, the n-type second cladding layer 6, theanti-cracking layer 5 and the n-type contact layer 4 are removed throughthe Ni mask by RIE or the like with etching gas of CF₄, for example,thereby forming the mesa portion having the thickness of about 70 μm asshown in FIG. 7. Thereafter the Ni mask is removed with hydrochloricacid or the like.

Finally, the p-side electrode 16 of Au/Pd is formed on the p-typecontact layer 15, as shown in FIG. 1. Further, the n-side electrode 17of Au/Ti is formed on the part of the surface of the n-type contactlayer 4 exposed by etching. The wafer formed in the aforementionedmanner is cleaved, for example, thereby forming a cavity structurehaving a cavity length of about 300 μm along the longitudinal directionof stripes. Thus, the nitride-based semiconductor laser device accordingto the first embodiment is fabricated.

In the method of fabricating the nitride-based semiconductor laserdevice according to the first embodiment, the mask layer 13 is employedas the mask for forming the current blocking layer 14 by selectivegrowth as hereinabove described, so that the current blocking layer 14can be formed only in the vicinity of the current path portion 12. Thus,strain applied to the current blocking layer 14 due to the differencebetween the lattice constants of the current blocking layer 14 and then-type contact layer 4 of n-type GaN formed with the large thickness ofabout 4 μm can be relaxed.

(Second Embodiment)

The structure of a nitride-based semiconductor laser device according toa second embodiment of the present invention is described with referenceto FIG. 8. The nitride-based semiconductor laser device according to thesecond embodiment is a real refractive index guided laser device. Whilethe current blocking layer 14 is selectively grown only in the vicinityof the current path portion 12 by using the mask layer 13 in theaforementioned first embodiment, a current blocking layer 33 isselectively grown on step portions 100 thereby forming parts of thecurrent blocking layer 33 having a smaller thickness than that in thevicinity of a current path portion 32 in regions not in the vicinity ofthe current path portion 32 in the second embodiment. The secondembodiment is now described in detail.

In the structure of the nitride-based semiconductor laser deviceaccording to the second embodiment, a buffer layer 22 of AlGaN having athickness of about 15 nm and an undoped GaN layer 23 having a thicknessof about 0.5 μm are formed on a sapphire (0001) plane substrate 21(hereinafter referred to as “sapphire substrate 21”). An n-type contactlayer 24 of n-type GaN having a mesa portion of about 10 μm in width anda thickness of about 4 μm is formed on the undoped GaN layer 23. Thesapphire substrate 21 is an example of the “substrate” according to thepresent invention, and the n-type contact layer 24 is an example of the“nitride-based semiconductor layer” according to the present invention.

An anti-cracking layer 25 of n-type In_(0.05)Ga_(0.95)N having athickness of about 0.1 μm, an n-type second cladding layer 26 ofSi-doped Al_(0.1)Ga_(0.9)N having a thickness of about 1 μm, an n-typefirst cladding layer 27 of Si-doped GaN having a thickness of about 50nm and an MQW emission layer 28 consisting of multiple quantum wells(MQW) of InGaN are formed on the mesa portion of the n-type contactlayer 24 to have a width of about 10 μm. The MQW emission layer 28 isformed by alternately stacking five barrier layers of undopedIn_(y)Ga_(1-y)N (In composition: y=0, i.e., GaN) each having a thicknessof about 4 nm and four well layers of undoped In_(x)Ga_(1-x)N (Incomposition: x=0.15) each having a thickness of about 4 nm. The MQWemission layer 28 is an example of the “emission layer” according to thepresent invention.

A p-type first cladding layer 29 of Mg-doped GaN having a width of about2 μm and a thickness of about 40 nm is formed substantially at thecenter of the upper surface of the MQW emission layer 28. A p-typesecond cladding layer 30 of Mg-doped Al_(v)Ga_(1-v)N (Al composition:v=0.08) having a width of about 2 μm and a thickness of about 0.45 μmand a cap layer 31 of p-type GaN having a width of about 2 μm and athickness of about 50 nm are formed to be substantially in contact withthe overall upper surface of the p-type first cladding layer 29. Thep-type first cladding layer 29, the p-type second cladding layer 30 andthe cap layer 31 form the current path portion 32 having a width W1(about 2 μm in the second embodiment).

Each of exposed parts (terraces) 28 a of the upper surface of the MQWemission layer 28 located on both sides of the current path portion 32has a width of about 4 μm. The step portions 100 of about 3 μm in heightare formed on the outer sides of the terraces 28 a. In other words, thestep portions 100 are formed on positions separating from the currentpath portion 32 by the width (about 4 μm) of the terraces 28 a. Thus,the step portions 100 are preferably formed on positions separating fromthe current path portion 32 by at least once and not more than threetimes (twice (about 4 μm) in this embodiment) the width (about 2 μm) ofthe current path portion 32. The p-type first cladding layer 29 and thep-type second cladding layer 30 are examples of the “cladding layer”according to the present invention.

A current blocking layer 33 of undoped Al_(w)Ga_(1-w)N (Al composition:w=0.3) is formed to cover partial side portions of the current pathportion 32, the upper surface of the MQW emission layer 28 and the stepportions 100. In this case, the part of the current blocking layer 33formed on the upper surface of the MQW emission layer 28 has a thicknessof about 3 μm on the terraces 28 a in the vicinity of the current pathportion 32 while having a smaller thickness on the step portions 100 ascompared with the thickness in the vicinity of the current path portion32. In this case, the distance W2 (about 10 μm) between the stepportions 100 including the current path portion 32 is set to at leastthree times and not more than seven times (five times in thisembodiment) the width W1 (about 2 μm) of the current path portion 32.

A p-type contact layer 34 of Mg-doped GaN having a thickness of about 1μm is formed to cover part of the upper surface of the current blockinglayer 33 in the vicinity of the current path portion 32 and the currentpath portion 32 (the cap layer 31) exposed on the current blocking layer33. Each of the layers 22 to 31, 33 and 34 has a wurtzite structure, andis formed by growth in the [0001] direction of the nitride-basedsemiconductor. Raw material gas for forming the layers 22 to 31, 33 and34 consisting of nitride semiconductors on the sapphire substrate 21 byMOVPE is prepared from trimethyl aluminum (TMAl), trimethyl gallium(TMGa), trimethyl indium (TMIn), NH₃, SiH₄ or cyclopentadienyl magnesium(Cp₂Mg), for example.

A p-side electrode 35 consisting of Au/Pd is formed on the p-typecontact layer 34 by stacking Pd and Au layers on the p-type contactlayer 34 in this order. An n-side electrode 36 consisting of Au/Ti isformed on the exposed surface part of the n-type contact layer 24 bystacking Ti and Au layers on the n-type contact layer 24 in this order.

According to the second embodiment, the current blocking layer 33 isformed to have the large thickness of about 3 μm in the vicinity of thecurrent path portion 32 and thinly formed on the step portions 100 notin the vicinity of the current path portion 32 as hereinabove described,so that strain applied to the current blocking layer 33 due to thedifference between the lattice constants of the current blocking layer33 and the n-type contact layer 24 of n-type GaN formed on the sapphiresubstrate 21 with the large thickness of about 4 μm easily concentratesto the thin regions (the step portions 100) of the current blockinglayer 33. Thus, lattice defects or cracks are easily caused in the thinregions of the current blocking layer 33 not in the vicinity of thecurrent path portion 32, whereby the current blocking layer 33 can beinhibited from formation of cracks or lattice defects in the vicinity ofthe current path portion 32. Consequently, the thickness of the currentblocking layer 33 can be increased in the vicinity of the current pathportion 32, thereby stabilizing transverse light confinement.

A method of fabricating the nitride-based semiconductor laser deviceaccording to the second embodiment is now described with reference toFIGS. 8 to 14.

As shown in FIG. 9, the buffer layer 22 of AlGaN having the thickness ofabout 15 nm, the undoped GaN layer 23 having the thickness of about 0.5μm, the n-type contact layer 24 of Si-doped GaN having the thickness ofabout 4 μm, the anti-cracking layer 25 of n-type In_(0.05)Ga_(0.95)Nhaving the thickness of about 0.1 μm, the n-type second cladding layer26 of Si-doped Al_(0.1)Ga_(0.9)N having the thickness of about 1 μm andthe n-type first cladding layer 27 of Si-doped GaN having the thicknessof about 50 nm are formed on the sapphire substrate 21 by MOVPE underthe atmospheric pressure under conditions similar to the growthconditions according to the first embodiment shown in FIG. 2.

Then, five undoped GaN barrier layers and four undopedIn_(0.15)Ga_(0.85)N well layers are alternately stacked on the n-typefirst cladding layer 27, thereby forming the MQW emission layer 28. Thep-type first cladding layer 29 of Mg-doped GaN having the thickness ofabout 40 nm, the p-type second cladding layer 30 of Mg-dopedAl_(v)Ga_(1-v)N (Al composition: v=0.08) having the thickness of about0.45 μm and the cap layer 31 of p-type GaN having the thickness of about50 nm are formed on the MQW emission layer 28.

Thereafter a striped Ni mask layer (not shown) having a width of about10 μm is formed on a prescribed region of the cap layer 31, as shown inFIG. 10. This Ni mask layer is employed as a mask for removing partialregions of the cap layer 31, the p-type second cladding layer 30, thep-type first cladding layer 29, the MQW emission layer 28, the n-typefirst cladding layer 27, the n-type second cladding layer 26, theanti-cracking layer 25 and the n-type contact layer 24 by etching withetching gas of CF₄, for example, thereby forming the step portions 100.Thereafter the Ni mask layer is removed.

Thereafter another striped Ni mask layer (not shown) having a width ofabout 2 μm is formed on the cap layer 31. This Ni mask layer is employedas a mask for etching the cap layer 31, the p-type second cladding layer30 and the p-type first cladding layer 29 by RIE or the like withetching gas of CF₄, for example, until the MQW emission layer 28 isexposed, and thereafter the Ni mask layer is removed. Thus, the currentpath portion (ridge portion) 32, having the width of about 2 μm,consisting of the p-type first cladding layer 29, the p-type secondcladding layer 30 and the cap layer 31 is formed as shown in FIG. 11. Inthis case, the terraces 28 a having the width of about 4 μm are formedon both sides of the current path portion 32 while exposing the MQWemission layer 28 on the upper surfaces thereof. Thereafter a mask layer37 of a silicon nitride such as Si₃N₄ having a width of about 2 μm and athickness of about 0.5 μm is formed only on the upper surface of thecurrent path portion 32 (the cap layer 31) by ECR plasma CVD, forexample.

As shown in FIG. 12, the current blocking layer 33 is selectively grownby low-pressure MOVPE with pressure of about 1×10⁴ Pa on the stepportions 100. Thus, the current blocking layer 33 of undoped AlGaN isformed to cover partial regions of the side portions of the current pathportion 32, the upper surface of the MQW emission layer 28, the sidesurfaces (the step portions 100) of the MQW emission layer 28, then-type first cladding layer 27, the n-type second cladding layer 26, theanti-cracking layer 25 and the n-type contact layer 24 and the uppersurface of the n-type contact layer 24. According to this selectivegrowth on the step portions 100, the part of the current blocking layer33 formed in the vicinity of the current path portion 32 on the MQWemission layer 28 has the large thickness of about 3 μm, while the partsformed on the step portions 100 have a smaller thickness than that inthe vicinity of the current path portion 32. Thereafter the mask layer37 is removed from the current path portion 32 (the cap layer 31).

As shown in FIG. 13, the p-type contact layer 34 of Mg-doped GaN havingthe thickness of about 1 μm is formed by low-pressure MOVPE withpressure of about 1×10⁴ Pa to cover part of the current blocking layer33 in the vicinity of the current path portion 32 and the current pathportion 32 (the cap layer 31) exposed on the current blocking layer 33.

Then, a striped Ni mask layer (not shown) having a width of about 70 μmand a thickness of about 3 μm to about 5 μm, for example, is formed on aprescribed region of the wafer through a metal mask by EB deposition.This Ni mask layer is employed as a mask for removing partial regions ofthe current blocking layer 33 and the n-type contact layer 24 by RIE orthe like with etching gas of CF₄, for example, thereby partiallyexposing the upper surface of the n-type contact layer 24 as shown inFIG. 14. Thereafter the aforementioned Ni mask layer is removed withhydrochloric acid or the like.

Finally, the p-side electrode 35 of Au/Pd is formed on the p-typecontact layer 34, as shown in FIG. 8. Further, the n-side electrode 36of Au/Ti is formed on the surface part of the n-type contact layer 24exposed by etching. The wafer formed in the aforementioned manner iscleaved, for example, thereby forming a cavity structure having a cavitylength of about 300 μm in the longitudinal direction of stripes. Thus,the nitride-based semiconductor laser device according to the secondembodiment is fabricated.

In the method of fabricating the nitride-based semiconductor laserdevice according to the second embodiment, the current blocking layer 33is selectively grown on the step portions 100 as hereinabove described,whereby crystallinity of the current blocking layer 33 can be improved.Due to the selective growth on the step portions 100, further, the thinregions of the current blocking layer 33 can be formed on the stepportions 100 not in the vicinity of the current path portion 32.Therefore, strain applied to the current blocking layer 33 due to thedifference between the lattice constants of the current blocking layer33 and the n-type contact layer 24 of n-type GaN having the largethickness of about 4 μm easily concentrates to the thin regions of thecurrent blocking layer 33. Thus, the current blocking layer 33 can beinhibited from formation of cracks or lattice defects in the vicinity ofthe current path portion 32.

(Third Embodiment)

The structure of a nitride-based semiconductor laser device according toa third embodiment of the present invention is described with referenceto FIG. 15. The nitride-based semiconductor laser device according tothe third embodiment has a real refractive index guided self-alignedstructure.

In the structure of the nitride-based semiconductor laser deviceaccording to the third embodiment, a buffer layer 42 of n-type AlGaNhaving a thickness of about 15 nm, an n-type GaN layer 43 of n-type GaNhaving a thickness of about 4 μm, an anti-cracking layer 44 of n-typeIn_(0.05)Ga_(0.95)N having a thickness of about 0.1 μm, an n-type secondcladding layer 45 of n-type AlGaN having a thickness of about 1 μm andan n-type first cladding layer 46 of n-type GaN having a thickness ofabout 50 nm are formed on an n-type Si (111) plane substrate 41(hereinafter referred to as “n-type Si substrate 41”).

An MQW emission layer 47 consisting of multiple quantum wells (MQW) ofInGaN is formed on the n-type first cladding layer 46. This MQW emissionlayer 47 is formed by alternately stacking five barrier layers ofundoped In_(y)Ga_(1-y)N (In composition: y=0, i.e., GaN) each having athickness of about 4 nm and four well layers of undoped In_(x)Ga_(1-x)N(In composition: x=0.15) each having a thickness of about 4 nm. Then-type Si substrate 41 is an example of the “substrate” according to thepresent invention, and the n-type GaN layer 43 is an example of the“nitride-based semiconductor layer” according to the present invention.The MQW emission layer 47 is an example of the “emission layer”according to the present invention.

A p-type first cladding layer 48 of Mg-doped GaN having a thickness ofabout 40 nm is formed on the MQW emission layer 47. A mask layer 49 of asilicon nitride such as Si₃N₄ having an opening of about 8 μm in widthis formed on a partial region of the upper surface of the p-type firstcladding layer 48. A current blocking layer 50 of undopedAl_(w)Ga_(1-w)N (Al composition: w=0.2) having an opening and athickness of about 3 μm is formed on the upper surface of the p-typefirst cladding layer 48 exposed in the opening of the mask layer 49 witha width W2 of about 8 μm. A p-type second cladding layer 52 of undopedAl_(v)Ga_(1-v)N (Al composition: v=0.08) having a thickness of about0.45 μm is formed on the p-type first cladding layer 48 in the openingof the current blocking layer 50. The p-type second cladding layer 52has an inverse mesa shape (inverse trapezoidal shape) and is so formedthat a surface closer to the p-type first cladding layer 48 has a widthW1 of about 2 μm and side surfaces thereof are in contact with the innerside surface of the opening of the current blocking layer 50. The p-typefirst cladding layer 48 is an example of the “first cladding layer”according to the present invention, and the p-type second cladding layer52 is an example of the “second cladding layer” according to the presentinvention.

A mask layer 51 of a silicon nitride such as Si₃N₄ is formed on theupper surface of the current blocking layer 50. A p-type contact layer53 of Mg-doped GaN having a thickness of about 3 μm to about 5 μm isformed on the p-type second cladding layer 52 and on the mask layer 51.The p-type second cladding layer 52 and the p-type contact layer 53 forma current path portion having the width W1 (about 2 μm in the thirdembodiment). The width (the total width of the current path portion andthe current blocking layer 50) W2 (about 8 μm) of the opening of themask layer 49 is set in the range of at least three times and not morethan seven times (four times in this embodiment) the width W1 (about 2μm) of the current path portion (the lower surface of the p-type secondcladding layer 52), for the following reason:

If the total width W2 of the current path portion and the currentblocking layer 50 is smaller than three times the width W1 of thecurrent path portion, the range of formation of the current blockinglayer 50 is so excessively reduced that transverse light confinement isinsufficient. If the total width W2 of the current path portion and thecurrent blocking layer 50 is larger than seven times the width W1 of thecurrent path portion, strain applied to the current blocking layer 50 isso increased as to cause a large number of crystal defects or cracks onthe current blocking layer 50. Therefore, the total width W2 of thecurrent path portion and the current blocking layer 50 is preferably setin the range of at least three times and not more than seven times thewidth W1 of the current path portion. Each of the layers 42 to 48, 50,52 and 53 has a wurtzite structure and is formed by growth in the [0001]direction of the nitride-based semiconductor.

A p-side electrode 54 of Au/Pd is formed on the p-type contact layer 53by stacking Pd and Au layers on the p-type contact layer 53 in thisorder. An n-side electrode 55 of Au/Ti is formed on the back surface ofthe n-type Si substrate 41 having conductivity by stacking Ti and Aulayers on the n-type Si substrate 41 in this order.

According to the third embodiment, as hereinabove described, the currentblocking layer 50 is formed in the range of the width W2 (about 8 μm) ofthe opening of the mask layer 49, so that the current blocking layer 50can be provided only in the vicinity of the current path portion. Thus,the width of the current blocking layer 50 is reduced as compared withthat formed in the vicinity of the current path portion and on theoverall surface excluding the region in the vicinity of the current pathportion. Therefore, strain applied to the current blocking layer 50 dueto the difference between the lattice constants of the current blockinglayer 50 and the n-type GaN layer 43 of n-type GaN formed on the Sisubstrate 41 with the large thickness of about 4 μm can be relaxed,whereby the current blocking layer 50 can be inhibited from formation ofcracks or lattice defects. Consequently, the thickness of the currentblocking layer 50 can be increased, thereby stabilizing transverse lightconfinement.

A method of fabricating the nitride-based semiconductor laser deviceaccording to the third embodiment is now described with reference toFIGS. 15 to 19.

As shown in FIG. 16, the buffer layer 42 of n-type AlGaN having thethickness of about 15 nm and the n-type GaN layer 43 of Si-doped GaNhaving the thickens of about 4 μm are formed on the n-type Si substrate41 by MOVPE under the atmospheric pressure while holding the substratetemperature at about 1150° C. Then, the anti-cracking layer 44 of n-typeIn_(0.05)Ga_(0.95)N having the thickness of about 0.1 μm is formed onthe n-type GaN layer 43 while holding the substrate temperature at about880° C. The n-type second cladding layer 45 of Si-dopedAl_(0.15)Ga_(0.85)N having the thickness of about 1 μm and the n-typefirst cladding layer 46 of Si-doped GaN having the thickness of about 50nm are formed on the anti-cracking layer 44 while holding the substratetemperature at about 1150° C.

Then, five undoped GaN barrier layers and four undopedIn_(0.15)Ga_(0.85)N well layers are alternately stacked on the n-typefirst cladding layer 46 while holding the substrate temperature at about880° C., thereby forming the MQW emission layer 47. The p-type firstcladding layer 48 of Mg-doped GaN having the thickness of about 40 nm isformed on the MQW emission layer 48 while holding the substratetemperature at about 1150° C.

Thereafter the striped mask layer 49 of a silicon nitride such as Si₃N₄having the opening of about 8 μm in width is formed on the upper surfaceof the p-type first cladding layer 48, as shown in FIG. 17. The masklayer 49 is employed as a mask for selectively growing undoped AlGaN (Alcomposition: 0.2) on the upper surface of the p-type first claddinglayer 48 exposed in the opening of the mask layer 49 by low-pressureMOVPE with pressure of about 1×10⁴ Pa, thereby forming the currentblocking layer 50 of undoped AlGaN (Al composition: 0.2) having thethickness of about 3 μm. In this case, the flow rate of NH₃ is set tothree times the flow rate of NH₃ employed for MOVPE under theatmospheric pressure while increasing the substrate temperature by about100° C., for example. When the current blocking layer 50 is grown undersuch conditions, undoped AlGaN is selectively grown upward from theupper surface of the p-type first cladding layer 48 exposed in theopening of the mask layer 49 while no undoped AlGaN is grown on the masklayer 49. Thus, the current blocking layer 50 is formed on the uppersurface of the p-type first cladding layer 48 exposed in the opening ofthe mask layer 49 within the range of the width W2 (see FIG. 15) ofabout 8 μm of the opening of the mask layer 49.

As shown in FIG. 18, the mask layer 51 of SiN is formed on a region ofthe upper surface of the current blocking layer 50 except the portionfor forming the current path portion. The mask layer 51 is employed as amask for etching the current blocking layer 50 with etching gas of CF₄,for example, until the upper surface of the p-type first cladding layer48 is exposed by a width of about 2 μm. Thus, an opening for serving asthe current path portion is formed in the current blocking layer 50.

As shown in FIG. 19, the p-type second cladding layer 52 of Mg-dopedAlGaN (Al composition: 0.08) is grown on the upper surface of the p-typefirst cladding layer 48 exposed in the opening of the current blockinglayer 50 by low-pressure MOVPE with pressure of about 1×10⁴ Pa. Thus,the p-type second cladding layer 52 having the width (bottom width) ofabout 2 μm is formed in a self-aligned manner. The p-type contact layer53 of Mg-doped GaN having the thickness of about 3 μm to about 5 μm isformed on the upper surface of the p-type second cladding layer 52 andon the mask layer 51.

Raw material gas for forming the layers 42 to 48, 50, 52 and 53consisting of nitride semiconductors on the n-type Si substrate 41 byMOVPE is prepared from trimethyl aluminum (TMAl), trimethyl gallium(TMGa), trimethyl indium (TMIn), NH₃, SiH₄ or cyclopentadienyl magnesium(Cp₂Mg), for example.

Finally, the p-side electrode 54 of Au/Pd is formed on the p-typecontact layer 53, as shown in FIG. 15. Further, the n-side electrode 55of Au/Ti is formed on the back surface of the n-type Si substrate 41having conductivity. The wafer formed in the aforementioned manner iscleaved, for example, thereby forming a cavity structure having a cavitylength of about 300 μm in the longitudinal direction of stripes. Thus,the self-aligned nitride-based semiconductor laser device according tothe third embodiment is fabricated.

In the method of fabricating the nitride-based semiconductor laserdevice according to the third embodiment, the current blocking layer 50having an opening is formed in the vicinity of the region of the uppersurface of the p-type first cladding layer 48 formed with the currentpath portion by using the mask layer 49 followed by formation of thep-type second cladding layer 52 and the p-type contact layer 53 formingthe current path portion on the p-type first cladding layer 48 in theopening of the current blocking layer 50, whereby the self-alignednitride-based semiconductor laser device can be easily formed with thecurrent blocking layer 50 provided only in the vicinity of the currentpath portion. Thus, the width of the current blocking layer 50 isreduced as compared with that formed on the overall surface, whichconsists of the vicinity of the current path portion and the regionexcluding the vicinity of the current path portion. Therefore, strainapplied to the current blocking layer 50 due to the difference betweenthe lattice constants of the current blocking layer 50 and the n-typeGaN layer 43 of n-type GaN formed with the large thickness of about 4 μmcan be relaxed, whereby the current blocking layer 50 can be inhibitedfro formation of cracks or lattice defects.

According to the third embodiment, the current blocking layer 50 isformed by selective growth by using the mask layer 49 serving for a maskof the selective growth as described above, whereby crystallinity of thecurrent blocking layer 50 can be improved in the self-alignednitride-based semiconductor laser device.

(Fourth Embodiment)

The structure of a nitride-based semiconductor laser device according toa fourth embodiment of the present invention is described with referenceto FIG. 20. According to the fourth embodiment, an n-type GaN substrateis employed for a self-aligned nitride-based semiconductor laser device.The fourth embodiment is now described in detail with reference to acomplex refractive index guided nitride-based semiconductor laserdevice.

In the structure of the nitride-based semiconductor laser deviceaccording to the fourth embodiment, an anti-cracking layer 62 of n-typeIn_(0.05)Ga_(0.95)N having a thickness of about 0.1 μm, an n-type secondcladding layer 63 of Si-doped Al_(0.3)Ga_(0.7)N having a thickness ofabout 1 μm, an n-type first cladding layer 64 of Si-doped GaN having athickness of about 50 nm and an MQW emission layer 65 consisting ofmultiple quantum wells (MQW) of InGaN are formed on an n-type GaN (0001)plane substrate 61 (hereinafter referred to as “n-type GaN substrate61”). The MQW emission layer 65 is formed by alternately stacking fivebarrier layers of undoped In_(y)Ga_(1-y)N (In composition: y=0, i.e.,GaN) each having a thickness of about 4 nm and four well layers ofundoped In_(x)Ga_(1-x)N (In composition: x=0.15) each having a thicknessof about 4 nm. The n-type GaN substrate 61 is an example of the “GaNsubstrate” according to the present invention, and the MQW emissionlayer 65 is an example of the “emission layer” according to the presentinvention.

A p-type first cladding layer 66 of Mg-doped GaN having a thickness ofabout 40 nm is formed on the MQW emission layer 65. A mask layer 67 of asilicon nitride such as Si₃N₄ having an opening of about 8 μm in widthis formed on a partial region of the upper surface of the p-type firstcladding layer 66. A current blocking layer 68 of undopedIn_(s)Ga_(1-s)N (In composition: s=0.15) having an opening with athickness of about 3 μm is formed on the upper surface of the p-typefirst cladding layer 66 exposed in the opening of the mask layer 67 witha width W2 of about 8 μm. A p-type second cladding layer 70 of Mg-dopedAl_(v)Ga_(1-v)N (Al composition: v=0.08) having a thickness of about0.45 μm is formed on the p-type first cladding layer 66 in the openingof the current blocking layer 68. The p-type second cladding layer 70 isformed to have an inverse mesa shape (inverse trapezoidal shape) so thata surface closer to the p-type first cladding layer 66 has a width W1 ofabout 2 μm. The side surfaces of the p-type second cladding layer 70 arein contact with the inner side surface of the opening of the currentblocking layer 68. The p-type first cladding layer 66 is an example ofthe “first cladding layer” according to the present invention, and thep-type second cladding layer 70 is an example of the “second claddinglayer” according to the present invention.

A mask layer 69 of a silicon nitride such as Si₃N₄ is formed on theupper surface of the current blocking layer 68. A p-type contact layer71 of Mg-doped GaN having a thickness of about 3 μm to about 5 μm isformed on the p-type second cladding layer 70 and on the mask layer 69.The p-type second cladding layer 70 and the p-type contact layer 71 forma current path portion having the width W1 (about 2 μm in the fourthembodiment). The width (the total width of the current path portion andthe current blocking layer 68) W2 (about 8 μm) of the opening of themask layer 67 is set in the range of at least three times and not morethan seven times the width W1 (about 2 μm) of the current path portion(the lower surface of the p-type second cladding layer 70). The reasonfor setting the width W2 in this range is similar to that in the firstembodiment. Each of the layers 62 to 66, 68, 70 and 71 has a wurtzitestructure, and is formed by growth in the [0001] direction of thenitride-based semiconductor.

A p-side electrode 72 of Au/Pd is formed on the p-type contact layer 71by stacking Pd and Au layers on the p-type contact layer 71 in thisorder. An n-side electrode 73 of Au/Pt/Ti/Al/Ti is formed on the backsurface of the n-type GaN substrate 61 having conductivity by stackingTi, Al, Ti, Pt and Au layers on the n-type GaN substrate 61 in thisorder so that the Ti layer is in contact with the n-type GaN substrate61.

According to the fourth embodiment, the current blocking layer 68 isformed in the range of the width W2 (about 8 μm) of the opening of themask layer 67 as hereinabove described, so that the current blockinglayer 68 can be formed only in the vicinity of the current path portion.Therefore, the width of the current blocking layer 68 is reduced ascompared with that formed on the overall surface, which consists of thevicinity of the current path portion and the region excluding thevicinity of the current path portion. Thus, strain applied to thecurrent blocking layer 68 due to the difference between the latticeconstants of the current blocking layer 68 and the n-type GaN substrate61 can be relaxed, whereby the current blocking layer 68 can beinhibited from formation of cracks or lattice defects. Consequently, thethickness of the current blocking layer 68 can be increased, therebystabilizing transverse light confinement.

A method of fabricating the nitride-based semiconductor laser deviceaccording to the fourth embodiment is now described with reference toFIGS. 20 to 24.

As shown in FIG. 21, the anti-cracking layer 62 of n-typeIn_(0.05)Ga_(0.95)N having the thickness of about 0.1 μm is formed onthe n-type GaN substrate 61 by MOVPE under the atmospheric pressurewhile holding the substrate temperature at about 880° C. The n-typesecond cladding layer 63 of Si-doped Al_(0.3)Ga_(0.7)N having thethickness of about 1 μm and the n-type first cladding layer 64 ofSi-doped GaN having the thickness of about 50 nm are formed on theanti-cracking layer 62 while holding the substrate temperature at about1150° C.

Then, five undoped GaN barrier layers and four undopedIn_(0.15)Ga_(0.85)N well layers are alternately stacked on the n-typefirst cladding layer 64 while holding the substrate temperature at about880° C., thereby forming the MQW emission layer 65. The p-type firstcladding layer 66 of Mg-doped GaN is formed on the MQW emission layer 65while holding the substrate temperature at about 1150° C.

As shown in FIG. 22, the striped mask layer 67 of a silicon nitride suchas Si₃N₄ having the opening of about 8 μm in width is formed on theupper surface of the p-type first cladding layer 66. The mask layer 67is employed as a mask for selectively growing undoped InGaN on the uppersurface of the p-type first cladding layer 66 exposed in the opening ofthe mask layer 67 by low-pressure MOVPE with pressure of about 1×10⁴ Pa,thereby forming the current blocking layer 68 of undoped InGaN havingthe thickness of about 3 μm. In this case, the flow rate of NH₃ is setto about three times the flow rate of NH₃ employed for MOVPE under theatmospheric pressure while increasing the substrate temperature by about100° C., for example. When the current blocking layer 68 is grown undersuch conditions, undoped InGaN is selectively grown upward on the uppersurface of the p-type first cladding layer 66 exposed in the opening ofthe mask layer 67 while no undoped InGaN is grown on the mask layer 67.Thus, the current blocking layer 68 is formed on the upper surface ofthe p-type first cladding layer 66 exposed on the opening of the masklayer 67 in the range of the width W2 (see FIG. 20) of about 8 μm of theopening of the mask layer 67.

As shown in FIG. 23, the mask layer 69 of SiN is formed on a region ofthe upper surface of the current blocking layer 68 except the portionforming the current path portion. The mask layer 69 is employed as amask for etching the current blocking layer 68 by RIE or the like withetching gas of CF₄, for example, until the upper surface of the p-typefirst cladding layer 66 is exposed by the width W1 (see FIG. 20) ofabout 2 μm. Thus, an opening for serving as the current path portion isformed between the current blocking layer 68 and the mask layer 69.

As shown in FIG. 24, the p-type second cladding layer 70 of Mg-dopedAlGaN (Al composition: 0.08) is grown on the upper surface of the p-typefirst cladding layer 66 exposed in the opening of the current blockinglayer 68 by low-pressure MOVPE with pressure of about 1×10⁴ Pa. Thus,the p-type second cladding layer 70 having the width (bottom width) ofabout 2 μm is formed in a self-aligned manner. The p-type contact layer71 of Mg-doped GaN having the thickness of about 3 μm to about 5 μm isformed on the upper surface of the p-type second cladding layer 70 andon the mask layer 69.

Raw material gas for forming the layers 62 to 66, 68, 70 and 71consisting of nitride semiconductors on the n-type GaN substrate 61 byMOVPE is prepared from trimethyl aluminum (TMAl), trimethyl gallium(TMGa), trimethyl indium (TMIn), NH₃, SiH₄ or cyclopentadienyl magnesium(Cp₂Mg), for example.

Finally, the p-side electrode 72 of Au/Pd is formed on the p-typecontact layer 71, as shown in FIG. 20. The n-side electrode 73 ofAu/Pt/Ti/Al/Ti is formed on the back surface of the n-type GaN substrate61 having conductivity so that the Ti layer is in contact with then-type GaN substrate 61. The wafer formed in the aforementioned manneris cleaved, for example, thereby forming a cavity structure having acavity length of about 300 μm in the longitudinal direction of stripes.Thus, the self-aligned nitride-based semiconductor laser deviceaccording to the fourth embodiment is fabricated.

In the method of fabricating the nitride-based semiconductor laserdevice according to the fourth embodiment, as hereinabove described, thecurrent blocking layer 68 having the opening is formed in the vicinityof the region formed with the current path portion on the upper surfaceof the p-type first cladding layer 66 by using the mask layer 67followed by formation of the p-type second cladding layer 70 and thep-type contact layer 71 forming the current path portion on the p-typefirst cladding layer 66 in the opening of the current blocking layer 68,whereby the self-aligned nitride-based semiconductor laser device can beeasily formed with the current blocking layer 68 provided only in thevicinity of the current path portion. Thus, the width of the currentblocking layer 68 is reduced as compared with that formed on the overallsurface, which consists of the vicinity of the current path portion andthe region excluding the vicinity of the current path portion.Therefore, strain applied to the current blocking layer 68 due to thedifference between the lattice constants of the current blocking layer68 and the n-type GaN substrate 61 can be relaxed.

In the fourth embodiment, further, the current blocking layer 68 isformed by selective growth by using the mask layer 67 as describedabove, whereby crystallinity of the current blocking layer 68 can beimproved in the self-aligned nitride-based semiconductor laser device.

(Fifth Embodiment)

FIG. 25 shows a real refractive index guided ridge nitride-basedsemiconductor laser device according to a fifth embodiment of thepresent invention. The structure of the nitride-based semiconductorlaser device according to the fifth embodiment is now described. Each ofthe following fifth to eleventh embodiments of the present invention isdescribed with reference to a current blocking layer formed by adielectric blocking layer and a semiconductor blocking layer formed onthe dielectric blocking layer.

In the structure of the nitride-based semiconductor laser deviceaccording to the fifth embodiment, an n-type contact layer 102 ofSi-doped GaN having a mesa portion with a thickness of about 4 μm isformed on a sapphire substrate 101. An n-type cladding layer 103 ofSi-doped AlGaN having a thickness of about 1 μm and an MQW emissionlayer 104 having a multiple quantum well (MQW) structure of InGaN areformed on the upper surface of the mesa portion of the n-type contactlayer 102. The MQW emission layer 104 is formed by alternately stackingthree quantum well layers of In_(x)Ga_(1-x)N each having a thickness ofabout 8 nm and four quantum barrier layers of In_(y)Ga_(1-y)N eachhaving a thickness of about 16 nm. In this MQW emission layer 104, x>y,and the MQW emission layer 104 is formed to satisfy x=0.13 and y=0.05 inthis embodiment. The MQW emission layer 104 is an example of the“emission layer” according to the present invention.

A p-type cladding layer 105 of Mg-doped Al_(v)Ga_(1-v)N (Al composition:v=0.08) having a projection portion of about 1.5 μm in width is formedon the MQW emission layer 104. The thickness of the projection portionof the p-type cladding layer 105 is about 0.4 μm, and the thickness of aflat portion excluding the projection portion is about 0.1 μm. A p-typefirst contact layer 106 of Mg-doped GaN having a width of about 1.5 μmand a thickness of about 0.01 μm is formed on the upper surface of theprojection portion of the p-type cladding layer 105. The projectionportion of the p-type cladding layer 105 and the p-type first contactlayer 106 form a current path portion (ridge portion) having a width W1of about 1.5 μm. The p-type cladding layer 105 is an example of the“cladding layer” according to the present invention.

A dielectric blocking layer 107 of SiN having a thickness of about 50 nmis formed to cover the side surfaces of the current path portion (ridgeportion), the flat portion of the p-type cladding layer 105, the sidesurfaces of the MQW emission layer 104, the n-type cladding layer 103and the n-type contact layer 102 and a partial region of the uppersurface of the n-type contact layer 102. The dielectric blocking layer107 is formed to have an opening 107 a for selective growth in thevicinity of the current path portion on the upper surface of the flatportion of the p-type cladding layer 105.

A semiconductor blocking layer 108 of Al_(w)Ga_(1-w)N (Al composition:w=0.15) having a thickness of about 0.25 μm is formed in the vicinity ofthe current path potion (ridge portion) on the upper surface of thedielectric blocking layer 107 to fill up the side portions of thecurrent path portion. The semiconductor blocking layer 108 is formedonly in the vicinity of the current path portion so that the total widthW2 of the semiconductor blocking layer 108 and the current path portion(ridge portion) is about 7.5 μm. The semiconductor blocking layer 108 isformed to be in contact with the p-type cladding layer 105 through theopening 107 a formed in the dielectric blocking layer 107. Thedielectric blocking layer 107 and the semiconductor blocking layer 108form a current blocking layer.

A p-type second contact layer 109 of Mg-doped GaN having a thickness ofabout 0.07 μm is formed on the current path portion (ridge portion), onthe semiconductor blocking layer 108 and on the dielectric blockinglayer 107 to fill up the current path portion and the semiconductorblocking layer 108 while covering a partial region on the upper surfaceof the dielectric blocking layer 107.

A p-side ohmic electrode 110 consisting of a Pt layer having a thicknessof about 1 nm and a Pd layer having a thickness of about 3 nm stacked onthe p-type second contact layer 109 in this order is formed on thep-type second contact layer 109. A p-side pad electrode 111 consistingof an Ni layer having a thickness of about 0.1 μm and an Au layer havinga thickness of about 3 μm stacked on the p-side ohmic electrode 110 inthis order is formed on a partial region of the upper surface of thep-side ohmic electrode 110. An n-side ohmic electrode 112 consisting ofa Ti layer having a thickness of about 10 nm and an Al layer having athickness of about 0.1 μm stacked on the n-type contact layer 102 inthis order is formed on the exposed surface of the n-type contact layer102. An n-side pad electrode 113 consisting of an Ni layer having athickness of about 0.1 μm and an Au layer having a thickness of about 3μm stacked on the n-side ohmic electrode 112 in this order is formed ona partial region of the upper surface of the n-side ohmic electrode 112.

According to the fifth embodiment, the current blocking layer is formedby the dielectric blocking layer 107 and the semiconductor blockinglayer 108 formed on the dielectric blocking layer 107 as hereinabovedescribed, whereby the semiconductor blocking layer 108 is in contactwith the upper surface of the p-type cladding layer 105 through theopening 107 a of the dielectric blocking layer 107 and hence the contactarea between the p-type cladding layer 105 and the semiconductorblocking layer 108 can be reduced. Therefore, strain applied to thesemiconductor blocking layer 108 due to the difference between thelattice constants of the p-type cladding layer 105 and the semiconductorblocking layer 108 can be relaxed, whereby the semiconductor blockinglayer 108 can be inhibited from formation of cracks or crystal defectssuch as dislocations. Further, the contact area between the p-typecladding layer 105 and the semiconductor blocking layer 108 can bereduced, whereby formation of crystal defects resulting from acontaminant on the interface between the p-type cladding layer 105 andthe semiconductor blocking layer 108 can also be suppressed. Inaddition, the dielectric blocking layer 107 can be interposed betweenthe semiconductor blocking layer 108 and the underlayer, whereby strainapplied to the semiconductor blocking layer 108 due to the differencebetween the lattice constants of the semiconductor blocking layer 108and the thick n-type contact layer 108 of GaN forming the underlayer canbe relaxed. The semiconductor blocking layer 108 can be inhibited fromformation of cracks or crystal defects such as dislocations also bythis.

According to the fifth embodiment, the semiconductor blocking layer 108can be inhibited from formation of cracks or crystal defects ashereinabove described, whereby the thickness of the current blockinglayer (the semiconductor blocking layer 108) can be increased so thatthe nitride-based semiconductor laser device can stabilize transverselight confinement.

According to the fifth embodiment, the semiconductor blocking layer 108is formed only in the vicinity of the current path portion ashereinabove described, whereby the region for forming the semiconductorblocking layer 108 is so reduced that strain applied to thesemiconductor blocking layer 108 due to the difference between thelattice constants of the p-type cladding layer 105 and the semiconductorblocking layer 108 can be further relaxed. The semiconductor blockinglayer 108 can be inhibited from formation of cracks or crystal defectsalso by this, whereby transverse light confinement can be furtherstabilized and the semiconductor blocking layer 108 can be formed withexcellent crystallinity.

According to the fifth embodiment, further, the semiconductor blockinglayer 108 is formed only in the vicinity of the current path portion,thereby reducing the capacitance between the current blocking layerconsisting of the semiconductor blocking layer 108 and the dielectricblocking layer 107 and the p-type cladding layer 105. Thus, a pulse foroperating the device can be quickly rise and fall, whereby anitride-based semiconductor laser device allowing high-speed pulsedoperation can be obtained.

According to the fifth embodiment, the thickness (about 50 nm) of thedielectric blocking layer 107 is set smaller than the thickness (about0.25 μm) of the semiconductor blocking layer 108 as hereinabovedescribed, whereby the semiconductor blocking layer 108 having higherthermal conductivity than the dielectric blocking layer 107 caneffectively radiate heat generated in the MQW emission layer 104.Consequently, excellent characteristics can be attained also inhigh-temperature operation or high-output operation of the nitride-basedsemiconductor laser device.

According to the fifth embodiment, the semiconductor blocking layer 108of Al_(w)Ga_(1-w)N is employed to absorb no light in the semiconductorblocking layer 108, whereby operating current of the nitride-basedsemiconductor laser device can be reduced.

A method of fabricating the nitride-based semiconductor laser deviceaccording to the fifth embodiment is now described with reference toFIGS. 25 to 32.

As shown in FIG. 26, the n-type contact layer 102 of Si-doped GaN havingthe thickness of about 4 μm and the n-type cladding layer 103 ofSi-doped AlGaN having the thickness of about 1 μm are formed on thesapphire substrate 101 by MOVPE. Three In_(y)Ga_(1-y)N quantum welllayers and four In_(y)Ga_(1-y)N quantum barrier layers are alternatelystacked on the n-type cladding layer 103 by MOVPE, thereby forming theMQW emission layer 104. The p-type cladding layer 105 of Mg-dopedAl_(v)Ga_(1-v)N (Al composition: v=0.08) having the thickness of about0.4 μm and the p-type first contact layer 106 of Mg-doped GaN having thethickness of about 0.01 μm are successively formed on the MQW emissionlayer 104 by MOVPE.

Thereafter an SiO₂ film (not shown) having a thickness of about 0.2 μmis formed to cover the overall upper surface of the p-type first contactlayer 106 by plasma CVD, and a mask layer 200 of SiO₂ is formed byphotolithography and etching, as shown in FIG. 27. This mask layer 200is employed as a mask for etching prescribed regions of the p-type firstcontact layer 106, the p-type cladding layer 105, the MQW emission layer104, the n-type cladding layer 103 and the n-type contact layer 102 bydry etching such as RIE (reactive ion etching) with etching gasconsisting of Cl₂. Thereafter the mask layer 200 is removed from thep-type first contact layer 106.

Then, an SiO₂ film (not shown) having a thickness of about 0.2 μm isformed by plasma CVD to cover the overall upper surface of the p-typefirst contact layer 106. Thereafter the SiO₂ film is patterned byphotolithography and dry etching such as RIE with etching gas of Cl₂ orwet etching employing an HF-based etchant thereby forming a mask layer201 of SiO₂, as shown in FIG. 28.

As shown in FIG. 29, partial regions of the p-type contact layer 106 andthe p-type cladding layer 105 are etched by using the mask layer 201serving as a mask by dry etching such as RIE with etching gas of Cl₂.Thus, the current path portion (ridge portion), consisting of theprojection portion of the p-type cladding layer 105 and the p-type firstcontact layer 106, having the width W1 of about 1.5 μm is formed.Thereafter the mask layer 201 is removed.

As shown in FIG. 30, the dielectric blocking layer 107 of SiN having thethickness of about 50 nm is formed by plasma CVD to substantially coverthe overall upper surface of the wafer, and thereafter the opening 107 ais formed in the dielectric blocking layer 107 by photolithography andetching. The opening 107 a is so formed that a partial region of theupper surface of the flat portion of the p-type cladding layer 105 isexposed in the vicinity of the current path portion.

As shown in FIG. 31, the semiconductor blocking layer 108 ofAl_(w)Ga_(1-w)N (Al composition: w=0.15) having the thickness of about0.25 μm is selectively grown on the upper surface of the p-type claddinglayer 105 exposed in the opening 107 a to cover the dielectric blockinglayer 107 formed on the side portions of the current path portion. Thus,the semiconductor blocking layer 108 is formed in the vicinity of thecurrent path portion so that the total width W2 of the semiconductorblocking layer 108 and the current path portion is about 7.5 μm. Thissemiconductor blocking layer 108 can be easily formed by controlling thetime for selective growth. Thereafter the portion of the dielectricblocking layer 107 located on the current path portion (the p-type firstcontact layer 106) is removed by photolithography and dry etching withetching gas of CF₄ or wet etching with an HF-based etchant.

As shown in FIG. 32, the p-type second contact layer 109 of Mg-doped GaNhaving the thickness of about 0.07 μm is formed on the dielectricblocking layer 107 by MOVPE to cover the upper surface of the currentpath portion (the p-type first contact layer 106) and the semiconductorblocking layer 108.

Finally, the p-side ohmic electrode 110 consisting of the Pt layerhaving the thickness of about 1 nm and the Pd layer having the thicknessof about 3 nm is formed on the p-type second contact layer 109 by vacuumdeposition, as shown in FIG. 25. The p-side pad electrode 111 consistingof the Ni layer having the thickness of about 0.1 μm and the Au layerhaving the thickness of about 3 μm is formed on the partial region ofthe upper surface of the p-side ohmic electrode 110. Further, thepartial region of the dielectric blocking layer 107 located on the uppersurface of the n-type contact layer 102 is removed by photolithographyand etching. The n-side ohmic electrode 112 consisting of the Ti layerhaving the thickness of about 10 nm and the Al layer having thethickness of about 0.1 μm is formed on the exposed surface of the n-typecontact layer 102. The n-side pad electrode 113 consisting of the Nilayer having the thickness of about 0.1 μm and the Au layer having thethickness of about 3 μm is formed on the partial region of the uppersurface of the n-side ohmic electrode 112. Thus, the nitride-basedsemiconductor laser device according to the fifth embodiment isfabricated.

In the method of fabricating the nitride-based semiconductor laserdevice according to the fifth embodiment, the semiconductor blockinglayer 108 is formed by selective growth as hereinabove described,whereby crystallinity of the semiconductor blocking layer 108 can beimproved. Further, the semiconductor blocking layer 108 is selectivelygrown from the opening 107 a provided in the vicinity of the currentpath portion, so that the semiconductor blocking layer 108 can be formedonly in the vicinity of the current path portion. Thus, strain appliedto the semiconductor blocking layer 108 due to the difference betweenthe lattice constants of the semiconductor blocking layer 108 and thep-type cladding layer 105 can be relaxed.

FIG. 33 is a perspective view showing a nitride-based semiconductorlaser device according to a modification of the fifth embodiment of thepresent invention. The nitride-based semiconductor laser deviceaccording to the modification of the fifth embodiment is a complexrefractive index guided ridge, laser device different from thenitride-based semiconductor laser device according to the fifthembodiment only in the material for a semiconductor blocking layer.According to the modification of the fifth embodiment, a semiconductorblocking layer 118 of In_(s)Ga_(1-s)N (In composition: s=0.18) having athickness of about 0.25 μm is formed in the vicinity of a current pathportion on the upper surface of a dielectric block layer 107 to fill upside portions of the current path portion so that the total width W2 ofthe semiconductor blocking layer 118 and the current path portion isabout 7.5 μm, as shown in FIG. 33.

In the modification of the fifth embodiment, a current blocking layer isformed by the dielectric blocking layer 107 and the semiconductorblocking layer 118 of InGaN formed on the dielectric blocking layer 107as hereinabove described, whereby transverse light confinement can beperformed by absorbing light in the semiconductor blocking layer 118.Thus, transverse light confinement can be stabilized also when formingthe semiconductor blocking layer 118 having a smaller thickness than asemiconductor blocking layer of AlGaN. The remaining effects of themodification of the fifth embodiment are similar to those of the fifthembodiment.

In fabrication of the aforementioned nitride-based semiconductor laserdevice according to the modification of the fifth embodiment, thesemiconductor blocking layer 118 of InGaN is grown under a lowertemperature as compared with the semiconductor blocking layer 108 ofAlGaN according to the fifth embodiment. The remaining steps are similarto those in the fifth embodiment. The semiconductor blocking layer 118of InGaN can be formed under a lower temperature as compared with thesemiconductor blocking layer 108 of AlGaN according to the fifthembodiment as described above, whereby an impurity (Mg) introduced intoa p-type cladding layer 105 can be prevented from diffusing into an MQWemission layer 104. Consequently, the nitride-based semiconductor laserdevice can be improved in reliability.

(Sixth Embodiment)

FIG. 34 shows a real refractive index guided ridge nitride-basedsemiconductor laser device according to a sixth embodiment of thepresent invention. While the semiconductor blocking layer 108 is formedonly in the vicinity of the current path portion (ridge portion) in theaforementioned fifth embodiment, a semiconductor blocking layer 121 isformed substantially on the overall upper surface of a p-type claddinglayer 105 in the sixth embodiment. The sixth embodiment is now describedin detail.

In the structure of the nitride-based semiconductor laser deviceaccording to the sixth embodiment, an n-type contact layer 102, ann-type cladding layer 103 and an MQW emission layer 104 are formed on asapphire substrate 101, similarly to the fifth embodiment. The p-typecladding layer 105 having a projection portion and a p-type firstcontact layer 106 are formed on the MQW emission layer 104. Theprojection portion of the p-type cladding layer 105 and the p-type firstcontact layer 106 form a current path portion (ridge portion). Thecompositions and the thicknesses of the layers 102 to 106 in the sixthembodiment are similar to those in the fifth embodiment.

A dielectric blocking layer 120 of SiN having a thickness of about 50 nmis formed to cover the side surfaces of the current path portion (ridgeportion), a flat portion of the p-type cladding layer 105, the sidesurfaces of the MQW emission layer 104, the n-type cladding layer 103and the n-type contact layer 102 and a partial region of the uppersurface of the n-type contact layer 102. According to the sixthembodiment, the dielectric blocking layer 120 is formed to have fouropenings 120 a for selective growth on the upper surface of the flatportion of the p-type cladding layer 105. The openings 120 a are formednot only in the vicinity of the ridge portion but also in the remainingregions.

The semiconductor blocking layer 121 of Al_(w)Ga_(1-w)N (Al composition:w=0.15) having a thickness of about 0.25 μm is formed substantially onthe overall upper surface of the dielectric blocking layer 120 formed onthe p-type cladding layer 105, to cover the side portions of the currentpath portion. In other words, the semiconductor blocking layer 121 isformed not only in the vicinity of the ridge portion but alsosubstantially on the overall upper surface of the p-type cladding layer105 according to the sixth embodiment. The semiconductor blocking layer121 is formed to be in contact with the p-type cladding layer 105through the openings 120 a provided in the dielectric blocking layer120. The dielectric blocking layer 120 and the semiconductor blockinglayer 121 form a current blocking layer.

A p-type second contact layer 122 of Mg-doped GaN having a thickness ofabout 0.07 μm is formed substantially on the overall upper surfaces ofthe current path portion (ridge portion) and the semiconductor blockinglayer 121.

A p-side ohmic electrode 123 consisting of a Pt layer having a thicknessof about 1 nm and a Pd layer having a thickness of about 3 nm stacked onthe p-type second contact layer 122 in this order is formed on thep-type second contact layer 122. A p-side pad electrode 124 consistingof an Ni layer having a thickness of about 0.1 μm and an Au layer havinga thickness of about 3 μm stacked on the p-side ohmic electrode 123 inthis order is formed on a partial region of the upper surface of thep-side ohmic electrode 123. An n-side ohmic electrode 125 consisting ofa Ti layer having a thickness of about 10 nm and an Al layer having athickness of about 0.1 μm stacked on the n-type contact layer 102 inthis order is formed on the exposed surface of the n-type contact layer102. An n-side pad electrode 126 consisting of an Ni layer having athickness of about 0.1 μm and an Au layer having a thickness of about 3μm stacked on the n-side ohmic electrode 125 in this order is formed ona partial region of the upper surface of the n-side ohmic electrode 125.

According to the sixth embodiment, the semiconductor blocking layer 121is formed substantially on the overall upper surface of the dielectricblocking layer 120 formed on the p-type cladding layer 105 ashereinabove described, whereby the p-type second contact layer 122formed on the semiconductor blocking layer 121 can be flattened. Thus,strain applied to the current path portion (ridge portion) can bereduced when assembling the nitride-based semiconductor laser device ona submount (heat sink) in a junction-down (j-down) system from the sideof the ridge portion. Consequently, the nitride-based semiconductorlaser device can be improved in reliability.

According to the sixth embodiment, further, the current blocking layeris formed by the dielectric blocking layer 120 and the semiconductorblocking layer 121 similarly to the fifth embodiment, whereby thesemiconductor blocking layer 121 is in contact with the upper surface ofthe p-type cladding layer 105 through the openings 120 a of thedielectric blocking layer 120 and hence the contact area between thep-type cladding layer 105 and the semiconductor blocking layer 121 canbe reduced. Therefore, strain applied to the semiconductor blockinglayer 121 due to the difference between the lattice constants of thep-type cladding layer 105 and the semiconductor blocking layer 121 canbe relaxed, whereby the semiconductor blocking layer 121 can beinhibited from formation of cracks or crystal defects such asdislocations. The contact area between the p-type cladding layer 105 andthe semiconductor blocking layer 121 can be reduced, thereby suppressingformation of crystal defects resulting from a contaminant on theinterface between the p-type cladding layer 105 and the semiconductorblocking layer 121. Further, the dielectric blocking layer 120 can beinterposed between the semiconductor blocking layer 121 and theunderlayer, whereby strain applied to the semiconductor blocking layer121 due to the difference between the lattice constants of thesemiconductor blocking layer 121 and the thick n-type contact layer 102of GaN forming the underlayer can be relaxed. The semiconductor blockinglayer 121 can be inhibited from formation of cracks or crystal defectssuch as dislocations also by this.

According to the sixth embodiment, the semiconductor blocking layer 121can be inhibited from formation of cracks or crystal defects ashereinabove described, whereby the thickness of the current blockinglayer (the semiconductor blocking layer 121) can be increased and thenitride-based semiconductor laser device can stabilize transverse lightconfinement as a result.

According to the sixth embodiment, further, the dielectric blockinglayer 120 is formed to have a thickness (about 50 nm) smaller than thethickness (about 0.25 μm) of the semiconductor blocking layer 121similarly to the fifth embodiment, whereby the semiconductor blockinglayer 121 having higher thermal conductivity than the dielectricblocking layer 120 can effectively radiate heat generated in the MQWemission layer 104. Consequently, excellent characteristics can beattained also in high-temperature operation or high-output operation ofthe nitride-based semiconductor light-emitting device.

According to the sixth embodiment, the semiconductor blocking layer 121of Al_(w)Ga_(1-w)N is employed similarly to the fifth embodiment, sothat the semiconductor blocking layer 121 absorbs no light and hence theoperating current of the nitride-based semiconductor light-emittingdevice can be reduced.

A method of fabricating the nitride-based semiconductor laser deviceaccording to the sixth embodiment is now described with reference toFIGS. 34 to 37.

As shown in FIG. 35, the n-type contact layer 102, the n-type claddinglayer 103, the MQW emission layer 104, the p-type cladding layer 105 andthe p-type first contact layer 106 are formed on the sapphire substrate101 by a method similar to that in the fifth embodiment shown in FIGS.26 to 29. Then, the dielectric blocking layer 120 of SiN having thethickness of about 50 nm is formed by plasma CVD to substantially coverthe overall upper surface of the wafer, followed by formation of thefour openings 120 a in the dielectric blocking layer 120 byphotolithography and dry etching with etching gas of CF₄ or wet etchingwith an HF-based etchant. The openings 120 a are formed to expose thepartial region of the upper surface of the flat portion of the p-typecladding layer 105.

As shown in FIG. 36, the semiconductor blocking layer 121 ofAl_(w)Ga_(1-w)N (Al composition: w=0.15) having the thickness of about0.25 μm is selectively grown on the upper surface of the p-type claddinglayer 105 exposed in the openings 120 a by MOVPE, to cover thedielectric blocking layer 120 formed on the side portions of the currentpath portion and on the upper surface of the p-type cladding layer 105.Thereafter the portion of the dielectric blocking layer 120 located onthe current path portion (the p-type first contact layer 106) removed byphotolithography and dry etching with etching gas of CF₄ or wet etchingwith an HF-based etchant.

As shown in FIG. 37, the p-type second contact layer 122 of Mg-doped GaNhaving the thickness of about 0.07 μm is formed substantially on theoverall upper surfaces of the current path portion (the p-type firstcontact layer 106) and the semiconductor blocking layer 121 by MOVPE.

Finally, the p-side ohmic electrode 123 and the p-side pad electrode 124are successively formed by vacuum deposition, as shown in FIG. 34. Thepartial region of the dielectric blocking layer 120 located on the uppersurface of the n-type contact layer 102 is removed by photolithographyand etching. The n-side ohmic electrode 125 and the n-side pad electrode126 are successively formed on the exposed surface of the n-type contactlayer 102. Thus, the nitride-based semiconductor laser device accordingto the sixth embodiment is fabricated.

In the method of fabricating the nitride-based semiconductor laserdevice according to the sixth embodiment, the semiconductor blockinglayer 121 is formed by selective growth as hereinabove described,whereby crystallinity of the semiconductor blocking layer 121 can beimproved.

FIG. 38 is a perspective view showing a nitride-based semiconductorlaser device according to a modification of the sixth embodiment of thepresent invention. The nitride-based semiconductor laser deviceaccording to the modification of the sixth embodiment is a complexrefractive index guided ridge laser device different from thenitride-based semiconductor laser device according to the sixthembodiment only in the material for a semiconductor blocking layer 127.In the modification of the sixth embodiment, the semiconductor blockinglayer 127 of In_(s)Ga_(1-s)N (In composition: s=0.18) having a thicknessof about 0.25 μm is formed to cover a dielectric blocking layer 120formed on the side portions of a current path portion and on the uppersurface of a p-type cladding layer 105, as shown in FIG. 38.

In the modification of the sixth embodiment, a current blocking layer isformed by the dielectric blocking layer 120 and the semiconductorblocking layer 127 of InGaN formed on the dielectric blocking layer 120as hereinabove described, whereby transverse light confinement can beperformed by absorbing light in the semiconductor blocking layer 127.Thus, transverse light confinement can be stabilized also when formingthe semiconductor blocking layer 127 having a smaller thickness than asemiconductor blocking layer of AlGaN. The remaining effects of themodification of the sixth embodiment are similar to those of the sixthembodiment.

In fabrication of the aforementioned nitride-based semiconductor laserdevice according to the modification of the sixth embodiment, thesemiconductor blocking layer 127 of InGaN is grown under a lowertemperature as compared with the semiconductor blocking layer 121 ofAlGaN according to the sixth embodiment. The remaining steps are similarto those in the sixth embodiment. The semiconductor blocking layer 127of InGaN can be formed under a lower temperature as compared with thesemiconductor blocking layer 121 of AlGaN according to the sixthembodiment as described above, whereby an impurity (Mg) introduced intothe p-type cladding layer 105 can be prevented from diffusing into anMQW emission layer 104. Consequently, the nitride-based semiconductorlaser device can be improved in reliability.

(Seventh Embodiment)

FIG. 39 shows a real refractive index guided self-aligned nitride-basedsemiconductor laser device according to a seventh embodiment of thepresent invention.

In the structure of the nitride-based semiconductor laser deviceaccording to the seventh embodiment, an n-type contact layer 102, ann-type cladding layer 103 and an MQW emission layer 104 are formed on asapphire substrate 101, similarly to the fifth embodiment. A p-typefirst cladding layer 130 of Mg-doped Al_(v)Ga_(1-v)N (Al composition:v=0.08) having a thickness of about 0.1 μm is formed on the MQW emissionlayer 104. The p-type first cladding layer 130 is an example of the“first cladding layer” according to the present invention. Thecompositions and the thicknesses of the layers 102 to 104 are similar tothose in the fifth embodiment.

A dielectric blocking layer 131 of SiN having a thickness of about 50 nmis formed to cover the upper surface of the p-type first cladding layer130, the side surfaces of the MQW emission layer 104, the n-typecladding layer 103 and the n-type contact layer 102 and a partial regionof the upper surface of the n-type contact layer 102. According to theseventh embodiment, the dielectric blocking layer 131 is formed to havefour openings 131 a and a central opening 131 b having a width of about1.5 μm for forming a current path portion. The openings 131 a are formednot only in the vicinity of the current path portion but also in theremaining regions.

A semiconductor blocking layer 132 of Al_(w)Ga_(1-w)N (Al composition:w=0.15) having a thickness of about 0.25 μm is formed on the dielectricblocking layer 131 formed on the upper surface of the p-type firstcladding layer 130 to have an opening of about 1.5 μm in width forforming the current path portion. According to the seventh embodiment,the semiconductor blocking layer 132 is formed not only in the vicinityof the current path portion but also substantially on the overall uppersurface of the p-type first cladding layer 130. The semiconductorblocking layer 132 is formed to be in contact with the p-type firstcladding layer 130 through the openings 131 a provided in the dielectricblocking layer 131. The dielectric blocking layer 131 and thesemiconductor blocking layer 132 form a current blocking layer.

A p-type second cladding layer 133 of Mg-doped Al_(v)Ga_(1-v)N (Alcomposition: v=0.08) having a thickness of about 0.3 μm is formed on thep-type first cladding layer 130 in the opening 131 b for forming thecurrent path portion of the current blocking layer (the dielectricblocking layer 131 and the semiconductor blocking layer 132) and on thesemiconductor blocking layer 132. The p-type second cladding layer 133is an example of the “second cladding layer” according to the presentinvention.

A p-type contact layer 134 of Mg-doped GaN having a thickness of about0.07 μm is formed substantially on the overall upper surface of thep-type second cladding layer 133. A p-side ohmic electrode 136consisting of a Pt layer having a thickness of about 1 nm and a Pd layerhaving a thickness of about 3 nm stacked on the p-type contact layer 134in this order is formed on the p-type contact layer 134. A p-side padelectrode 137 consisting of an Ni layer having a thickness of about 0.1μn and an Au layer having a thickness of about 3 μm stacked on thep-side ohmic electrode 136 in this order is formed on a partial regionof the upper surface of the p-side ohmic electrode 136. An n-side ohmicelectrode 138 consisting of a Ti layer having a thickness of about 10 nmand an Al layer having a thickness of about 0.1 μm stacked on the n-typecontact layer 102 in this order is formed on the exposed surface of then-type contact layer 102. An n-side pad electrode 139 consisting of anNi layer having a thickness of about 0.1 μm and an Au layer having athickness of about 3 μm stacked on the n-side ohmic electrode 138 inthis order is formed on a partial region of the upper surface of then-side ohmic electrode 138.

A protective film 135 of SiN having a thickness of about 0.1 μm isformed to cover the side portions of the p-side ohmic electrode 136, thep-type contact layer 134, the p-type second cladding layer 133 and thesemiconductor blocking layer 132 and the dielectric blocking layer 131.

According to the seventh embodiment, the p-type second cladding layer133 is formed to extend onto the upper surface of the semiconductorblocking layer 132 as hereinabove described, whereby the area of theupper surface of the p-type second cladding layer 133 can be increased.Thus, contact resistance between the p-type second cladding layer 133and the p-type contact layer 134 formed thereon can be reduced.

According to the seventh embodiment, further, the p-type second claddinglayer 133 is formed on the semiconductor blocking layer 132 havingexcellent crystallinity as hereinabove described, whereby the p-typesecond cladding layer 133 can be obtained with excellent crystallinity.Consequently, the p-type second cladding layer 133 is improved inthermal conductivity, whereby excellent characteristics can be attainedalso in high-temperature operation or high-output operation of thenitride-based semiconductor light-emitting diode.

According to the seventh embodiment, the p-type second cladding layer133 is formed on the semiconductor blocking layer 132 having excellentcrystallinity as hereinabove described, whereby the p-type secondcladding layer 133 can be improved in crystallinity and the carrierconcentration thereof can be increased. Consequently, operating voltageof the nitride-based semiconductor laser device can be reduced. Theremaining effects of the seventh embodiment are similar to those of thesixth embodiment.

A method of fabricating the nitride-based semiconductor laser deviceaccording to the seventh embodiment is now described with reference toFIGS. 39 to 45.

As shown in FIG. 40, the n-type contact layer 102, the n-type claddinglayer 103 and the MQW emission layer 104 are formed on the sapphiresubstrate 101, similarly to the method of fabricating the nitride-basedsemiconductor laser device according to the fifth embodiment. Thecompositions and the thicknesses of the layers 102 to 104 are similar tothose in the fifth embodiment. The p-type first cladding layer 130 ofMg-doped Al_(v)Ga_(1-v)N (Al composition: v=0.08) having the thicknessof about 0.1 μm is formed on the MQW emission layer 104 by MOVPE.

Then, an SiO₂ film (not shown) having a thickness of about 0.2 μm isformed by plasma CVD to cover the overall upper surface of the p-typefirst cladding layer 103, followed by formation of a patterned masklayer 200 of SiO₂ by photolithography and etching, as shown in FIG. 41.This mask layer 200 is employed as, a mask for etching prescribedregions of the p-type first cladding layer 130, the MQW emission layer104, the n-type cladding layer 103 and the n-type contact layer 102 bydry etching such as RIE with etching gas of Cl₂. Thereafter the masklayer 200 is removed from the p-type first cladding layer 130.

As shown in FIG. 42, the dielectric blocking layer 131 of SiN having thethickness of about 50 nm is formed by plasma CVD to substantially coverthe overall upper surface of the wafer, followed by formation of thefour openings 131 a and the opening 131 b having the width of about 1.5μm for forming the current path portion in the dielectric blocking layer131 by photolithography and dry etching with etching gas of CF₄ or wetetching with an HF-based etchant. The openings 131 a and 131 b areformed to expose the partial region on the upper surface of the p-typefirst cladding layer 130.

As shown in FIG. 43, the semiconductor blocking layer 132 ofAl_(w)Ga_(1-w)N (Al composition: w=0.15) having the thickness of about0.25 μm is selectively grown substantially on the overall upper surfaceof the p-type first cladding layer 130 exposed in the openings 131 a and131 b. Thereafter an SiO₂ film (not shown) having a thickness of about0.2 μm is formed by plasma CVD to substantially cover the overall uppersurface of the semiconductor blocking layer 132, followed by formationof a patterned mask layer 202 of SiO₂ by photolithography and etching,as shown in FIG. 43.

As shown in FIG. 44, the mask layer 202 is employed as a mask foretching the semiconductor blocking layer 132 formed on the opening 131 bby dry etching such as RIE with etching gas of Cl₂. Thus, the openinghaving the width of about 1.5 μm for forming the current path portion isformed in the semiconductor blocking layer 132. Thereafter the masklayer 202 is removed from the semiconductor blocking layer 132.

As shown in FIG. 45, the p-type second cladding layer 133 of Mg-dopedAl_(v)Ga_(1-v)N (Al composition: v=0.08) is grown on the upper surfaceof the p-type first cladding layer 130 exposed in the opening of thecurrent blocking layer (the dielectric blocking layer 131 and thesemiconductor blocking layer 132) by MOVPE. Thus, the p-type secondcladding layer 133 having the width of about 1.5 μm is formed in theopening of the current blocking layer in a self-aligned manner. Thep-type second cladding layer 133 is formed to have the thickness ofabout 0.3 μm on the upper surface of the semiconductor blocking layer132. The p-type contact layer 134 of Mg-doped GaN having the thicknessof about 0.07 μm is formed on the upper surface of the p-type secondcladding layer 133 by MOVPE.

Finally, an SiN film (not shown) having a thickness of about 50 nm isformed to substantially cover the overall upper surface of the wafer.Thereafter the protective film 135 of SiN having the shape shown in FIG.39 is formed by photolithography and dry etching with etching gas of CF₄or wet etching with an HF-based etchant.

As shown in FIG. 39, the p-side ohmic electrode 136 and the p-side padelectrode 137 are successively formed on the p-type contact layer 134 byvacuum deposition. The partial region of the dielectric blocking layer131 located on the upper surface of the n-type contact layer 102 isremoved by photolithography and etching. The n-side ohmic electrode 138and the n-side pad electrode 139 are successively formed on the exposedsurface of the n-type contact layer 102. Thus, the nitride-basedsemiconductor laser device according to the seventh embodiment isfabricated.

In the method of fabricating the nitride-based semiconductor laserdevice according to the seventh embodiment, the semiconductor blockinglayer 132 is formed by selective growth as hereinabove described,whereby crystallinity of the semiconductor blocking layer 132 can beimproved.

FIG. 46 is a perspective view showing a nitride-based semiconductorlaser device according to a modification of the seventh embodiment ofthe, present invention. The nitride-based semiconductor laser deviceaccording to the modification of the seventh embodiment is a complexrefractive index guided self-aligned nitride-based semiconductor laserdevice different from the nitride-based semiconductor laser deviceaccording to the seventh embodiment only in the material for asemiconductor blocking layer 142. In the modification of the seventhembodiment, the semiconductor blocking layer 142 of In_(s)Ga_(1-s)N (Incomposition: s=0.18) having a thickness of about 0.25 μm is formed on adielectric blocking layer 131 to have an opening of about 1.5 μm inwidth for forming a current path portion, as shown in FIG. 46.

In the modification of the seventh embodiment, a current blocking layeris formed by the dielectric blocking layer 131 and the semiconductorblocking layer 142 of InGaN formed on the dielectric blocking layer 131as hereinabove described, whereby transverse light confinement can beperformed by absorbing light in the semiconductor blocking layer 142.Thus, transverse light confinement can be stabilized also when formingthe semiconductor blocking layer 142 having a smaller thickness than asemiconductor blocking layer of AlGaN. The remaining effects of themodification of the seventh embodiment are similar to those of theseventh embodiment.

In fabrication of the aforementioned nitride-based semiconductor laserdevice according to the modification of the seventh embodiment, thesemiconductor blocking layer 142 of InGaN is grown under a lowertemperature as compared with the semiconductor blocking layer 132 ofAlGaN according to the seventh embodiment. The remaining steps aresimilar to those in the seventh embodiment. The semiconductor blockinglayer 142 of InGaN can be formed under a lower temperature as comparedwith the semiconductor blocking layer 132 of AlGaN according to theseventh embodiment as described above, whereby an impurity (Mg)introduced into a p-type cladding layer 130 can be prevented fromdiffusing into an MQW emission layer 104. Consequently, thenitride-based semiconductor laser device can be improved in reliability.

(Eighth Embodiment)

FIG. 47 shows a real refractive index guided self-aligned nitride-basedsemiconductor laser device according to an eighth embodiment of thepresent invention. While the semiconductor blocking layer 132 is formedup to the region not in the vicinity of the current path portion in theaforementioned seventh embodiment, a semiconductor blocking layer 151according to the eighth embodiment is formed only in the vicinity of acurrent path portion. The eighth embodiment is now described in detail.

In the structure of the nitride-based semiconductor laser deviceaccording to the eighth embodiment, an n-type contact layer 102, ann-type cladding layer 103, an MQW emission layer 104 and a p-type firstcladding layer 130 are formed on a sapphire substrate 101, similarly tothe seventh embodiment. The compositions and the thicknesses of thelayers 102 to 104 and 130 are similar to those in the seventhembodiment.

A dielectric blocking layer 150 of SiN having a thickness of about 50 nmis formed to cover the upper surface of the p-type first cladding layer130, the side surfaces of the MQW emission layer 104, the n-typecladding layer 103 and the n-type contact layer 102 and a partial regionof the upper surface of the n-type contact layer 102. According to theeighth embodiment, the dielectric blocking layer 150 is formed to havetwo openings 150 a for selective growth and a central opening 150 bhaving a width W1 of about 1.5 μm for forming the current path portion.

The semiconductor blocking layer 151 of Al_(w)Ga_(1-w)N (Al composition:w=0.15) having a thickness of about 0.25 μm and a width W2 of about 7.5μm is formed in the vicinity of the current path portion on thedielectric blocking layer 150 to have an opening of about 1.5 μm inwidth for forming the current path portion. The semiconductor blockinglayer 151 is formed to be in contact with the p-type first claddinglayer 130 through the openings 150 a provided in the dielectric blockinglayer 150. The dielectric blocking layer 150 and the semiconductorblocking layer 151 form a current blocking layer.

A p-type second cladding layer 152 of Mg-doped Al_(v)Ga_(1-v)N (Alcomposition: v=0.08) having a thickness of about 0.3 μm is formed on thep-type first cladding layer 130 in the opening 150 b for forming thecurrent path portion of the current blocking layer (the dielectricblocking layer 150 and the semiconductor blocking layer 151) and on thedielectric blocking layer 150. The p-type second cladding layer 152 isan example of the “second cladding layer” according to the presentinvention.

A p-type contact layer 153 of Mg-doped GaN having a thickness of about0.07 μm is formed substantially on the overall upper surface of thep-type second cladding layer 152. A p-side ohmic electrode 155consisting of a Pt layer having a thickness of about 1 nm and a Pd layerhaving a thickness of about 3 nm stacked on the p-type contact layer 153in this order is formed on the p-type contact layer 153. A p-side padelectrode 156 consisting of an Ni layer having a thickness of about 0.1μm and an Au layer having a thickness of about 3 μm stacked on thep-side ohmic electrode 155 in this order is formed on a partial regionof the upper surface of the p-side ohmic electrode 155. An n-side ohmicelectrode 157 consisting of a Ti layer having a thickness of about 10 nmand an Al layer having a thickness of about 0.1 μm stacked on the n-typecontact layer 102 in this order is formed on the exposed surface of then-type contact layer 102. An n-side pad electrode 158 consisting of anNi layer having a thickness of about 0.1 μm and an Au layer having athickness of about 3 μm stacked on the n-side ohmic electrode 157 inthis order is formed on a partial region of the upper surface of then-side ohmic electrode 157.

A protective film 154 of SiN having a thickness of about 0.1 μm isformed to cover the side portions of the p-side ohmic electrode 155, thep-type contact layer 153, the p-type second cladding layer 152 and thesemiconductor blocking layer 151 and the dielectric blocking layer 150.

According to the eighth embodiment, the p-type second cladding layer 152is formed to extend onto the upper surface of the semiconductor blockinglayer 151 as hereinabove described, whereby the area of the uppersurface of the p-type second cladding layer 152 can be increased. Thus,contact resistance between the p-type second cladding layer 152 and thep-type contact layer 153 formed thereon can be reduced.

According to the eighth embodiment, further, the p-type second claddinglayer 152 is formed on the semiconductor blocking layer 151 havingexcellent crystallinity as hereinabove described, whereby the p-typesecond cladding layer 152 can be obtained with excellent crystallinity.Consequently, the p-type second cladding layer 152 is improved inthermal conductivity, whereby excellent characteristics can be attainedalso in high-temperature operation or high-output operation of thenitride-based semiconductor light-emitting diode.

According to the eighth embodiment, the p-type second cladding layer 152is formed on the semiconductor blocking layer 151 having excellentcrystallinity as hereinabove described, whereby the p-type secondcladding layer 152 can be improved in crystallinity and the carrierconcentration thereof can be increased. Consequently, operating voltageof the nitride-based semiconductor laser device can be reduced. Theremaining effects of the eighth embodiment are similar to those of thefifth embodiment.

A method of fabricating the nitride-based semiconductor laser deviceaccording to the eighth embodiment is now described with reference toFIGS. 47 to 51.

As shown in FIG. 48, the n-type contact layer 102, the n-type claddinglayer 103, the MQW emission layer 104 and the p-type first claddinglayer 130 are formed on the sapphire substrate 101, similarly to themethod of fabricating the nitride-based semiconductor laser deviceaccording to the fifth embodiment.

As shown in FIG. 48, the dielectric blocking layer 150 of SiN having thethickness of about 50 nm is formed by plasma CVD to substantially coverthe overall upper surface of the wafer, followed by formation of the twoopenings 150 a by photolithography and dry etching with etching gas ofCF₄ or wet etching with an HF-based etchant. The openings 150 a areformed to expose the partial region on the upper surface of the p-typefirst cladding layer 130.

As shown in FIG. 49, the semiconductor blocking layer 151 ofAl_(w)Ga_(1-w)N (Al composition: w=0.15) having the thickness of about0.25 μm is selectively grown on the upper surface of the p-type firstcladding layer 130 exposed in the openings 150 a to cover the dielectricblocking layer 150. The semiconductor blocking layer 151 is formed onlyin the vicinity of the current path potion to have the opening of thewidth W1 of about 1.5 μm for forming the current path portion so thatthe total width W2 of the current path portion and the semiconductorblocking layer 151 is about 7.5 μm. This semiconductor blocking layer151 can be easily formed by controlling the time for selective growth.

Thereafter an SiO₂ film (not shown) having a thickness of about 0.2 μmis formed by plasma CVD to cover the overall upper surface of the wafer.Then, the SiO₂ film and the dielectric blocking layer 150 are patternedby photolithography and etching. Thus, the dielectric blocking layer 150having the opening 150 b of the width W1 of about 1.5 μm for forming thecurrent path portion is formed under a mask layer 203 of SiO₂ having anopening for forming the current path portion, as show in FIG. 50.

As shown in FIG. 51, the p-type second cladding layer 152 of Mg-dopedAl_(v)Ga_(1-v)N (Al composition: v=0.08) is grown on the upper surfaceof the p-type first cladding layer 130 exposed in the opening of thecurrent blocking layer (the dielectric blocking layer 150 and thesemiconductor blocking layer 151) by MOVPE. Thus, the p-type secondcladding layer 152 having the width W1 of about 1.5 μm is formed in theopening of the current blocking layer in a self-aligned manner. Thep-type second cladding layer 152 is formed to have the thickness ofabout 0.3 μm on the upper surface of the semiconductor blocking layer151. The p-type contact layer 153 of Mg-doped GaN having the thicknessof about 0.07 μm is formed on the upper surface of the p-type secondcladding layer 152 by MOVPE.

Finally, an SiN film (not shown) having a thickness of about 50 nm isformed to substantially cover the overall upper surface of the wafer.Thereafter the protective film 154 of SiN having the shape shown in FIG.47 is formed by photolithography and dry etching with etching gas of CF₄or wet etching with an HF-based etchant.

As shown in FIG. 47, the p-side ohmic electrode 155 and the p-side padelectrode 156 are successively formed on the p-type contact layer 153 byvacuum deposition. The partial region of the dielectric blocking layer150 located on the upper surface of the n-type contact layer 102 isremoved by photolithography and etching. The n-side ohmic electrode 157and the n-side pad electrode 158 are successively formed on the exposedsurface of the n-type contact layer 102. Thus, the nitride-basedsemiconductor laser device according to the eighth embodiment isfabricated.

In the method of fabricating the nitride-based semiconductor laserdevice according to the eighth embodiment, the semiconductor blockinglayer 151 is formed by selective growth as hereinabove described,whereby crystallinity of the semiconductor blocking layer 151 can beimproved.

FIG. 52 is a perspective view showing a nitride-based semiconductorlaser device according to a modification of the eighth embodiment of thepresent invention. The nitride-based semiconductor laser deviceaccording to the modification of the eighth embodiment is a complexrefractive index guided self-aligned nitride-based semiconductor laserdevice different from the nitride-based semiconductor laser deviceaccording to the eighth embodiment only in the material for asemiconductor blocking layer 159. In the modification of the eighthembodiment, the semiconductor blocking layer 159 of In_(s)Ga_(1-s)N (Incomposition: s=0.18) having a thickness of about 0.25 μm and a width ofabout 3 μm is formed on a dielectric blocking layer 150 formed on theupper surface of a p-type first cladding layer 130 with a width W2 ofabout 7.5 μm to have an opening of a width W1 of about 1.5 μm forforming a current path portion, as shown in FIG. 52.

In the modification of the eighth embodiment, a current blocking layeris formed by the dielectric blocking layer 150 and the semiconductorblocking layer 159 of InGaN formed on the dielectric blocking layer 150as hereinabove described, whereby transverse light confinement can beperformed by absorbing light in the semiconductor blocking layer 159.Thus, transverse light confinement can be stabilized also when formingthe semiconductor blocking layer 159 having a smaller thickness than asemiconductor blocking layer of AlGaN.

In fabrication of the aforementioned nitride-based semiconductor laserdevice according to the modification of the eighth embodiment, thesemiconductor blocking layer 159 of InGaN is grown under a lowertemperature as compared with the semiconductor blocking layer 151 ofAlGaN according to the eighth embodiment. The remaining steps aresimilar to those in the eighth embodiment. The semiconductor blockinglayer 159 of InGaN can be formed under a lower temperature as comparedwith the semiconductor blocking layer 151 of AlGaN according to theeighth embodiment as described above, whereby an impurity (Mg)introduced into a p-type cladding layer 130 can be prevented fromdiffusing into an MQW emission layer 104. Consequently, thenitride-based semiconductor laser device can be improved in reliability.

(Ninth Embodiment)

FIG. 53 shows a real refractive index guided ridge nitride-basedsemiconductor laser device according to a ninth embodiment of thepresent invention. While the semiconductor blocking layer is formed tobe in contact with the p-type cladding layer located in the opening ofthe dielectric blocking layer in each of the aforementioned first toeighth embodiments, a semiconductor blocking layer 161 is formed to bein contact with a p-type cladding layer 105 on side surfaces of acurrent path portion in the ninth embodiment. The ninth embodiment isnow described in detail.

In the structure of the nitride-based semiconductor laser deviceaccording to the ninth embodiment, an n-type contact layer 102, ann-type cladding layer 103 and an MQW emission layer 104 are formed on asapphire substrate 101, similarly to the fifth embodiment. The p-typecladding layer 105 having a projection portion and a p-type firstcontact layer 106 are formed on the MQW emission layer 104. Theprojection portion of the p-type cladding layer 105 and the p-type firstcontact layer 106 form the current path portion (ridge portion). Thecompositions and the thicknesses of the layers 102 to 106 in the ninthembodiment are similar to those in the fifth embodiment.

The dielectric blocking layer 160 of SiN having a thickness of about 50nm is formed to cover a flat portion of the p-type cladding layer 105,the side surfaces of the MQW emission layer 104, the n-type claddinglayer 103 and the n-type contact layer 102 and a partial region of theupper surface of the n-type contact layer 102.

The semiconductor blocking layer 161 of Al_(w)Ga_(1-w)N (Al composition:w=0.15) having a thickness of about 0.25 μm is formed substantially onthe overall upper surface of the dielectric blocking layer 160 formed onthe p-type cladding layer 105, to cover the side surfaces of the currentpath portion. The dielectric blocking layer 160 and the semiconductorblocking layer 161 form a current blocking layer.

A p-type second contact layer 162 of Mg-doped GaN having a thickness ofabout 0.07 μm is formed substantially on the overall upper surfaces ofthe current path portion (ridge portion) and the semiconductor blockinglayer 161.

A p-side ohmic electrode 163 consisting of a Pt layer having a thicknessof about 1 nm and a Pd layer having a thickness of about 3 nm stacked onthe p-type second contact layer 162 in this order is formed on thep-type second contact layer 162. A p-side pad electrode 164 consistingof an Ni layer having a thickness of about 0.1 μm and an Au layer havinga thickness of about 3 μm stacked on the p-side ohmic electrode 163 inthis order is formed on a partial region of the upper surface of thep-side ohmic electrode 163. An n-side ohmic electrode 165 consisting ofa Ti layer having a thickness of about 10 nm and an Al layer having athickness of about 0.1 μm stacked on the n-type contact layer 102 inthis order is formed on the exposed surface of the n-type contact layer102. An n-side pad electrode 166 consisting of an Ni layer having athickness of about 0.1 μm and an Au layer having a thickness of about 3μm stacked on the n-side ohmic electrode 165 in this order is formed ona partial region of the upper surface of the n-side ohmic electrode 165.

According to the ninth embodiment, the semiconductor blocking layer 161is formed to be in contact with the side surfaces of the current pathportion (ridge portion) as hereinabove described, whereby the contactportions between the semiconductor blocking layer 161 and the p-typecladding layer 105 can be limited to the side surfaces of the currentpath portion (ridge portion). Thus, strain applied to the semiconductorblocking layer 161 can 10. be further relaxed. Consequently, variouseffects at least equivalent to those of the sixth embodiment areattained.

A method of fabricating the nitride-based semiconductor laser deviceaccording to the ninth embodiment is now described with reference toFIGS. 53 to 56. According to the ninth embodiment, the layers 102 to 106are formed similarly to those in the nitride-based semiconductor laserdevice according to the fifth embodiment shown in FIGS. 26 to 29.

As shown in FIG. 54, the n-type contact layer 102, the n-type claddinglayer 103, the MQW emission layer 104, the p-type cladding layer 105 andthe p-type first contact layer 106 are formed on the sapphire substrate101 by a method similar to that in the fifth embodiment. Then, thedielectric blocking layer 160 of SiN having the thickness of about 50 nmis formed by plasma CVD to substantially cover the overall upper surfaceof the wafer. Thereafter the portions of the dielectric blocking layer160 located on the side surfaces of the current path portion are removedby photolithography and dry etching with etching gas of CF₄ or wetetching with an HF-based etchant.

As shown in FIG. 55, the semiconductor blocking layer 161 ofAl_(w)Ga_(1-w)N (Al composition: w=0.15) having the thickness of about0.25 μm is selectively grown from the exposed side surfaces of thecurrent path portion (ridge portion) by MOVPE, to cover the dielectricblocking layer 120 formed on the upper surface of the p-type claddinglayer 105.

Thereafter the portion of the dielectric blocking layer 160 located onthe current path portion (the p-type first contact layer 106) is removedby photolithography and dry etching with etching gas of CF₄ or wetetching with an HF-based etchant, as shown in FIG. 56. The p-type secondcontact layer 162 of Mg-doped GaN having the thickness of about 0.07 μmis formed substantially on the overall upper surfaces of the currentpath portion (the p-type first contact layer 106) and the semiconductorblocking layer 161 by MOVPE.

Finally, the p-side ohmic electrode 163 and the p-side pad electrode 164are successively formed on the p-type second contact layer 162 by vacuumdeposition, as shown in FIG. 53. The partial region of the dielectricblocking layer 160 located on the upper surface of the n-type contactlayer 102 is removed by photolithography and etching. The n-side ohmicelectrode 165 and the n-side pad electrode 166 are successively formedon the exposed surface of the n-type contact layer 102. Thus, thenitride-based semiconductor laser device according to the ninthembodiment is fabricated.

In the method of fabricating the nitride-based semiconductor laserdevice according to the ninth embodiment, the semiconductor blockinglayer 161 is formed by selective growth as hereinabove described,whereby crystallinity of the semiconductor blocking layer 161 can beimproved.

FIG. 57 is a perspective view showing a nitride-based semiconductorlaser device according to a modification of the ninth embodiment of thepresent invention. The nitride-based semiconductor laser deviceaccording to the modification of the ninth embodiment is a complexrefractive index guided ridge laser device different from thenitride-based semiconductor laser device according to the ninthembodiment only in the material for a semiconductor blocking layer 167.In the modification of the ninth embodiment, the semiconductor blockinglayer 167 of In_(s)Ga_(1-s)N (In composition: s=0.18) having a thicknessof about 0.25 μm is formed substantially on the overall upper surface ofa dielectric blocking layer 160 formed on a p-type cladding layer 105 tocover the side surfaces of a current path portion, as shown in FIG. 57.

In the modification of the ninth embodiment, a current blocking layer isformed by the dielectric blocking layer 160 and the semiconductorblocking layer 167 of InGaN formed on the dielectric blocking layer 160as hereinabove described, whereby transverse light confinement can beperformed by absorbing light in the semiconductor blocking layer 167.Thus, transverse light confinement can be stabilized also when formingthe semiconductor blocking layer 167 having a smaller thickness than asemiconductor blocking layer of AlGaN. The remaining effects of themodification of the ninth embodiment are similar to those of the ninthembodiment.

In fabrication of the aforementioned nitride-based semiconductor laserdevice according to the modification of the ninth embodiment, thesemiconductor blocking layer 167 of InGaN is grown under a lowertemperature as compared with the semiconductor blocking layer 161 ofAlGaN according to the ninth embodiment. The remaining steps are similarto those in the ninth embodiment. The semiconductor blocking layer 167of InGaN can be formed under a lower temperature as compared with thesemiconductor blocking layer 161 of AlGaN according to the ninthembodiment as described above, whereby an impurity (Mg) introduced intothe p-type cladding layer 105 can be prevented from diffusing into anMQW emission layer 104. Consequently, the nitride-based semiconductorlaser device can be improved in reliability.

(Tenth Embodiment)

FIG. 58 shows a real refractive index guided ridge nitride-basedsemiconductor laser device according to a tenth embodiment of thepresent invention. While the semiconductor blocking layer 161 is formedup to the region not in the vicinity of the current path portion in theaforementioned ninth embodiment, a semiconductor blocking layer 171 isformed only in the vicinity of a current path portion in the tenthembodiment. The tenth embodiment is now described in detail.

In the structure of the nitride-based semiconductor laser deviceaccording to the tenth embodiment, an n-type contact layer 102, ann-type cladding layer 103 and an MQW emission layer 104 are formed on asapphire substrate 101, similarly to the ninth embodiment. A p-typecladding layer 105 having a projection portion and a p-type firstcontact layer 106 are formed on the MQW emission layer 104. Theprojection portion of the p-type cladding layer 105 and the p-type firstcontact layer 106 form the current path portion (ridge portion) having awidth W1 of about 1.5 μm. The compositions and the thicknesses of thelayers 102 to 106 in the tenth embodiment are similar to those in thefifth embodiment.

A dielectric blocking layer 170 of SiN having a thickness of about 50 nmis formed to cover a flat portion of the p-type cladding layer 105, theside surfaces of the MQW emission layer 104, the n-type cladding layer103 and the n-type contact layer 102 and a partial region of the uppersurface of the n-type contact layer 102.

The semiconductor blocking layer 171 of Al_(w)Ga_(1-w)N (Al composition:w=0.15) having a thickness of about 0.25 μm is formed in the vicinity ofthe current path portion (ridge portion) on the upper surface of thedielectric blocking layer 170, to cover the side portions of the currentpath portion. The semiconductor blocking layer 171 is formed only in thevicinity of the current path portion, so that the total width W2 of thesemiconductor blocking layer 171 and the current path portion is about7.5 μm. The dielectric blocking layer 170 and the semiconductor blockinglayer 171 form a current blocking layer.

A p-type second contact layer 172 of Mg-doped GaN having a thickness ofabout 0.07 μm is formed on the semiconductor blocking layer 171 locatedon a flat portion of the p-type cladding layer 105, to cover the uppersurface of the current path portion (ridge portion) and thesemiconductor blocking layer 171.

A p-side ohmic electrode 173 consisting of a Pt layer having a thicknessof about 1 nm and a Pd layer having a thickness of about 3 nm stacked onthe p-type second contact layer 172 in this order is formed on thep-type second contact layer 172. A p-side pad electrode 174 consistingof an Ni layer having a thickness of about 0.1 μm and an Au layer havinga thickness of about 3 μm stacked on the p-side ohmic electrode 173 inthis order is formed on a partial region of the upper surface of thep-side ohmic electrode 173. An n-side ohmic electrode 175 consisting ofa Ti layer having a thickness of about 10 nm and an Al layer having athickness of about 0.1 μm stacked on the n-type contact layer 102 inthis order is formed on the exposed surface of the n-type contact layer102. An n-side pad electrode 176 consisting of an Ni layer having athickness of about 0.1 μm and an Au layer having a thickness of about 3μm stacked on the n-side ohmic electrode 175 in this order is formed ona partial region of the upper surface of the n-side ohmic electrode 175.

According to the tenth embodiment, the semiconductor blocking layer 171is formed to be in contact with the side surfaces of the current pathportion (the p-type cladding layer 105 and the p-type first contactlayer 106) as hereinabove described, whereby the contact portionsbetween the semiconductor blocking layer 171 and the p-type claddinglayer 105 can be limited to the side surfaces of the current pathportion (ridge portion). Thus, strain applied to the semiconductorblocking layer 171 can be further relaxed. Further, the semiconductorblocking layer 171 is formed only in the vicinity of the current pathportion, thereby reducing the capacitance between the current blockinglayer consisting of the semiconductor blocking layer 171 and thedielectric blocking layer 170 and the p-type cladding layer 105. Thus, apulse for operating the device can be quickly rise and fall, whereby anitride-based semiconductor laser device allowing high-speed pulsedoperation can be obtained. The remaining effects of the tenth embodimentare similar to those of the fifth embodiment.

A method of fabricating the nitride-based semiconductor laser deviceaccording to the tenth embodiment is now described with reference toFIGS. 58 to 60.

As shown in FIG. 59, the n-type contact layer 102, the n-type claddinglayer 103, the MQW emission layer 104, the p-type cladding layer 105 andthe p-type first contact layer 106 are formed on the sapphire substrate101 by a method similar to that in the fifth embodiment shown in FIGS.26 to 29. Then, the dielectric blocking layer 170 of SiN having thethickness of about 50 nm is formed by plasma CVD to substantially coverthe overall upper surface of the wafer. Thereafter the portions of thedielectric blocking layer 170 located on the side surfaces of thecurrent path portion are removed by photolithography and dry etchingwith etching gas of CF₄ or wet etching with an HF-based etchant.

The semiconductor blocking layer 171 of Al_(w)Ga_(1-w)N (Al composition:w=0.15) having the thickness of about 0.25 μm is selectively grown byMOVPE in the vicinity of the current path portion on the upper surfaceof the dielectric blocking layer 170 from the exposed side surfaces ofthe current path portion (ridge portion). In this case, thesemiconductor blocking layer 171 is formed only in the vicinity of thecurrent path portion so that the total width W2 of the semiconductorblocking layer 171 and the current path portion is about 7.5 μm. Thissemiconductor blocking layer 171 can be easily formed by controlling thetime for selective growth.

Thereafter the portion of the dielectric blocking layer 170 located onthe current path portion (the p-type first contact layer 106) is removedby photolithography and dry etching with etching gas of CF₄ or wetetching with an HF-based etchant, as shown in FIG. 60. The p-type secondcontact layer 172 of Mg-doped GaN having the thickness of about 0.07 μmis formed to cover the upper surface of the current path portion (thep-type first contact layer 106) and the semiconductor blocking layer 161by MOVPE.

Finally, the p-side ohmic electrode 173 and the p-side pad electrode 174are successively formed on the p-type second contact layer 172 by vacuumdeposition, as shown in FIG. 58. The partial region of the dielectricblocking layer 170 located on the upper surface of the n-type contactlayer 102 is removed by photolithography and etching. The n-side ohmicelectrode 175 and the n-side pad electrode 176 are successively formedon the exposed surface of the n-type contact layer 102. Thus, thenitride-based semiconductor laser device according to the tenthembodiment is fabricated.

In the method of fabricating the nitride-based semiconductor laserdevice according to the tenth embodiment, the semiconductor blockinglayer 171 is formed by selective growth as hereinabove described,whereby crystallinity of the semiconductor blocking layer 171 can beimproved.

FIG. 61 is a perspective view showing a nitride-based semiconductorlaser device according to a modification of the tenth embodiment of thepresent invention. The nitride-based semiconductor laser deviceaccording to the modification of the tenth embodiment is a complexrefractive index guided ridge laser device different from thenitride-based semiconductor laser device according to the tenthembodiment only in the material for a semiconductor blocking layer 177.In the modification of the tenth embodiment, the semiconductor blockinglayer 177 of In_(s)Ga_(1-s)N (In composition: s=0.18) having a thicknessof about 0.25 μm and a width W2 of about 7.5 μm is formed in thevicinity of a current path portion on the upper surface of a dielectricblocking layer 170 to cover the side surfaces of the current pathportion, as shown in FIG. 61.

In the modification of the tenth embodiment, a current blocking layer isformed by the dielectric blocking layer 170 and the semiconductorblocking layer 177 of InGaN formed on the dielectric blocking layer 170as hereinabove described, whereby transverse light confinement can beperformed by absorbing light in the semiconductor blocking layer 177.Thus, transverse light confinement can be stabilized also when formingthe semiconductor blocking layer 177 having a smaller thickness than asemiconductor blocking layer of AlGaN. The remaining effects of themodification of the tenth embodiment are similar to those of the tenthembodiment.

In fabrication of the aforementioned nitride-based semiconductor laserdevice according to the modification of the tenth embodiment, thesemiconductor blocking layer 177 of InGaN is grown under a lowertemperature as compared with the semiconductor blocking layer 171 ofAlGaN according to the tenth embodiment. The remaining steps are similarto those in the tenth embodiment. The semiconductor blocking layer 177of InGaN can be formed under a lower temperature as compared with thesemiconductor blocking layer 171 of AlGaN according to the tenthembodiment as described above, whereby an impurity (Mg) introduced intoa p-type cladding layer 105 can be prevented from diffusing into an MQWemission layer 104. Consequently, the nitride-based semiconductor laserdevice can be improved in reliability.

(Eleventh Embodiment)

FIG. 62 shows a real refractive index guided ridge nitride-basedsemiconductor laser device according to an eleventh embodiment of thepresent invention. While a sapphire substrate is employed in each of theaforementioned first to third and fifth to tenth embodiments, a GaNsubstrate 181 having conductivity is employed in the eleventhembodiment. The eleventh embodiment is now described in detail.

In the structure of the nitride-based semiconductor laser deviceaccording to the eleventh embodiment, an n-type contact layer 182 ofSi-doped GaN having a thickness of about 4 μm, an n-type cladding layer183 of Si-doped AlGaN having a thickness of about 1 μm and an MQWemission layer 184 having a multiple quantum well (MQW) structure ofInGaN are formed on the GaN substrate 181. The MQW emission layer 184 isformed by alternately stacking three quantum well layers ofIn_(x)Ga_(1-x)N each having a thickness of about 8 nm and four quantumbarrier layers of In_(y)Ga_(1-y)N each having a thickness of about 16nm. In this MQW emission layer 184, x>y, and the MQW emission layer 184is formed to satisfy x=0.13 and y=0.05 according to this embodiment. TheMQW emission layer 184 is an example of the “emission layer” accordingto the present invention.

A p-type cladding layer 185 of Mg-doped Al_(v)Ga_(1-v)N (Al composition:v=0.08) having a projection portion of about 1.5 μm in width is formedon the MQW emission layer 184. The thickness of the projection portionof the p-type cladding layer 185 is about 0.4 μm, and the thickness of aflat portion excluding the projection portion is about 0.1 μm. A p-typefirst contact layer 186 of Mg-doped GaN having a width of about 1.5 μmand a thickness of about 0.01 μm is formed on the upper surface of theprojection portion of the p-type cladding layer 185. The projectionportion of the p-type cladding layer 185 and the p-type first contactlayer 186 form a current path portion (ridge portion) having a width W1of about 1.5 μm. The p-type cladding layer 185 is an example of the“cladding layer” according to the present invention.

A dielectric blocking layer 187 of SiN having a thickness of about 50 nmis formed to cover the side surfaces of the current path portion (ridgeportion) and the upper surface of the flat portion of the p-typecladding layer 184. The dielectric blocking layer 187 is formed to havean opening 187 a in the vicinity of the current path portion on theupper surface of the flat portion of the p-type cladding layer 185.

A semiconductor blocking layer 188 of Al_(w)Ga_(1-w)N (Al composition:w=0.15) having a thickness of about 0.25 μm and a width W2 of about 7.5μm is formed in the vicinity of the current path potion (ridge portion)on the upper surface of the dielectric blocking layer 187 to fill up theside portions of the current path portion. The semiconductor blockinglayer 188 is formed only in the vicinity of the current path portion sothat the total width W2 of the semiconductor blocking layer 188 and thecurrent path portion is about 7.5 μm. The semiconductor blocking layer188 is formed to be in contact with the p-type cladding layer 185through the opening 187 a formed in the dielectric blocking layer 187.The dielectric blocking layer 187 and the semiconductor blocking layer188 form a current blocking layer.

A p-type second contact layer 189 of Mg-doped GaN having a thickness ofabout 0.07 μm is formed on the dielectric blocking layer 187 to coverthe upper surface of the current path portion (the p-type first contactlayer 186) and the semiconductor blocking layer 188.

A p-side ohmic electrode 190 consisting of a Pt layer having a thicknessof about 1 nm and a Pd layer having a thickness of about 3 nm stacked onthe p-type second contact layer 189 in this order is formed on thep-type second contact layer 189. A p-side pad electrode 191 consistingof an Ni layer having a thickness of about 0.1 μm and an Au layer havinga thickness of about 3 μm stacked on the p-side ohmic electrode 190 inthis order is formed on a partial region of the upper surface of thep-side ohmic electrode 190. An n-side ohmic electrode 192 consisting ofa Ti layer having a thickness of about 10 nm and an Al layer having athickness of about 0.1 μm stacked on the GaN substrate 181 in this orderis formed on the back surface of the GaN substrate 181 havingconductivity. An n-side pad electrode 113 consisting of an Ni layerhaving a thickness of about 0.1 μm and an Au layer having a thickness ofabout 3 μm stacked on the n-side ohmic electrode 192 in this order isformed on a partial region of the back surface of the n-side ohmicelectrode 192.

According to the eleventh embodiment, effects similar to those of thefifth embodiment can be attained also when forming the current blockinglayer consisting of the dielectric blocking layer 187 and thesemiconductor blocking layer 188 on the GaN substrate 181 havingconductivity.

A method of fabricating the nitride-based semiconductor laser deviceaccording to the eleventh embodiment is now described with reference toFIGS. 62 to 67.

As shown in FIG. 63, the n-type contact layer 182 of Si-doped GaN havingthe thickness of about 4 μm, the n-type cladding layer 183 of Si-dopedAlGaN having the thickness of about 1 μm and the MQW emission layer 184are formed on the GaN substrate 181 by MOVPE. The p-type cladding layer185 of Mg-doped Al_(v)Ga_(1-v)N (Al composition: v=0.08) having thethickness of about 0.4 μm and the p-type first contact layer 186 ofMg-doped GaN having the thickness of about 0.01 μm are successivelyformed on the MQW emission layer 184 by MOVPE. Thereafter an SiO₂ film(not shown) having a thickness of about 0.2 μm is formed to cover theoverall upper surface of the p-type first contact layer 186 by plasmaCVD. Thereafter the SiO₂ film is patterned by photolithography and dryetching with etching gas of CF₄ or wet etching with an HF-based etchant,thereby forming a mask layer 204 of SiO₂ as shown in FIG. 63.

Thereafter the mask layer 204 is employed as a mask for etching partialregions of the p-type first contact layer 186 and the p-type claddinglayer 185 by dry etching such as RIE with etching gas consisting of Cl₂,as shown in FIG. 64. Thus, the current path portion (ridge portion),consisting of the projection portion of the p-type cladding layer 185and the p-type first contact layer 186, having the width W1 of about 1.5μm is formed. Thereafter the mask layer 204 is removed.

As shown in FIG. 65, the dielectric blocking layer 187 of SiN having thethickness of about 50 nm is formed by plasma CVD to substantially coverthe overall upper surface of the wafer, and thereafter the opening 187 ais formed in the dielectric blocking layer 187 by photolithography andetching. The opening 187 a is so formed that a partial region of theupper surface of the flat portion of the p-type cladding layer 185 isexposed in the vicinity of the current path portion.

As shown in FIG. 66, the semiconductor blocking layer 188 ofAl_(w)Ga_(1-w)N (Al composition: w=0.15) having the thickness of about0.25 μm is selectively grown on the upper surface of the p-type claddinglayer 185 exposed in the opening 187 a by MOVPE to cover the portions ofthe dielectric blocking layer 187 formed on the side portions of thecurrent path portion. The semiconductor blocking layer 188 is formedonly in the vicinity of the current path portion so that the total widthW2 of the semiconductor blocking layer 188 and the current path portionis about 7.5 μm. This semiconductor blocking layer 188 can be easilyformed by controlling the time for selective growth. Thereafter theportion of the dielectric blocking layer 187 located on the current pathportion (the p-type first contact layer 186) is removed byphotolithography and dry etching with etching gas of CF₄ or wet etchingwith an HF-based etchant, as shown in FIG. 67.

Then, the p-type second contact layer 189 of Mg-doped GaN having thethickness of about 0.07 μm is formed on the dielectric blocking layer187 by MOVPE to cover the upper surface of the current path portion (thep-type first contact layer 186) and the semiconductor blocking layer188.

Finally, the p-side ohmic electrode 190 and the p-side pad electrode 191are successively formed on the p-type second contact layer 189 by vacuumdeposition, as shown in FIG. 62. Further, the n-side ohmic electrode 192and the n-side pad electrode 193 are successively formed on the backsurface of the GaN substrate 181 having conductivity. Thus, thenitride-based semiconductor laser device according to the eleventhembodiment is fabricated.

In the method of fabricating the nitride-based semiconductor laserdevice according to the eleventh embodiment, the semiconductor blockinglayer 188 is formed by selective growth as hereinabove described,whereby crystallinity of the semiconductor blocking layer 188 can beimproved. Further, the semiconductor blocking layer 188 is selectivelygrown from the opening 187 a provided in the vicinity of the currentpath portion, so that the semiconductor blocking layer 188 can be formedonly in the vicinity of the current path portion. Thus, strain appliedto the semiconductor blocking layer 188 due to the difference betweenthe lattice constants of the semiconductor blocking layer 188 and thep-type cladding layer 185 can be relaxed.

FIG. 68 is a perspective view showing a nitride-based semiconductorlaser device according to a modification of the eleventh embodiment ofthe present invention. The nitride-based semiconductor laser deviceaccording to the modification of the eleventh embodiment is a complexrefractive index guided ridge laser device different from thenitride-based semiconductor laser device according to the eleventhembodiment only in the material for a semiconductor blocking layer 198.According to the modification of the eleventh embodiment, thesemiconductor blocking layer 198 of In_(s)Ga_(1-s)N (In composition:s=0.18) having a thickness of about 0.25 μm and a width W2 of about 7.5μm is formed to cover a dielectric blocking layer 187 formed on sideportions of a current path portion (ridge portion) and the upper surfaceof a p-type cladding layer 185, as shown in FIG. 68.

In the modification of the eleventh embodiment, a current blocking layeris formed by the dielectric blocking layer 187 and the semiconductorblocking layer 198 of InGaN formed on the dielectric blocking layer 187as hereinabove described, whereby transverse light confinement can beperformed by absorbing light in the semiconductor blocking layer 198.Thus, transverse light confinement can be stabilized also when formingthe semiconductor blocking layer 198 having a smaller thickness than asemiconductor blocking layer of AlGaN. The remaining effects of themodification of the eleventh embodiment are similar to those of theeleventh embodiment.

In fabrication of the aforementioned nitride-based semiconductor laserdevice according to the modification of the eleventh embodiment, thesemiconductor blocking layer 198 of InGaN is grown under a lowertemperature as compared with the semiconductor blocking layer 188 ofAlGaN according to the eleventh embodiment. The remaining steps aresimilar to those in the eleventh embodiment. The semiconductor blockinglayer 198 of InGaN can be formed under a lower temperature as comparedwith the semiconductor blocking layer 188 of AlGaN according to theeleventh embodiment as described above, whereby an impurity (Mg)introduced into a p-type cladding layer 185 can be prevented fromdiffusing into an MQW emission layer 184. Consequently, thenitride-based semiconductor laser device can be improved in reliability.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

For example, a high reflectivity film or low reflectivity film such as adielectric multilayer film formed by stacking layers of Si₃N₄, SiO₂,Al₂O₃ or TiO₂ may further be formed on the cavity surface of thenitride-based semiconductor laser device formed according to each of theaforementioned first to eleventh embodiments.

While the present invention is applied to the nitride-basedsemiconductor laser device in each of the aforementioned first toeleventh embodiments, the present invention is not restricted to thisbut also applicable to a surface emission type semiconductor laserdevice, for example. Assuming that B represents the diameter of anemission region in this case, a mask layer having a substantiallycircular opening (preferably having a diameter 3B to 7B) may be formedaround the emission region for forming a current blocking layer onlyaround the emission region in the opening of the mask layer, forexample. When a step portion is formed around a substantially circularterrace (flat portion) (preferably having a diameter 3B to 7B) aroundthe emission region for thereafter selectively growing a currentblocking layer on the step portion, a portion of the current blockinglayer having a small thickness can be formed on the step portion toenclose the emission layer. In this case, a dielectric blocking layermay be formed around the emission region for forming a semiconductorblocking layer on this dielectric blocking layer. The present inventionis also applicable to a superluminescent light-emitting diode device orthe like.

While a sapphire substrate, an n-type Si substrate or an n-type GaNsubstrate is employed in each of the aforementioned first to eleventhembodiments, the present invention is not restricted to this but aninsulator substrate such as a spinel substrate, a group 3–5semiconductor substrate such as a GaAs substrate, a GaP substrate or anInP substrate, an SiC substrate or a substrate of a boron compoundexpressed as MB₂ (M: metallic element such as Al, Ti, Zr, Hf, V, Nb, Taor Cr) may alternatively be employed.

While InGaN is employed as the material for the MQW emission layer ineach of the aforementioned first to eleventh embodiments, the presentinvention is not restricted to this but an emission layer mayalternatively be prepared from a material having a band gap smaller thanthose of an n-type first cladding layer and an n-type second claddinglayer. Particularly in a device provided with an emission layer having aquantum well structure of AlGaN, GaN or AlGaN/GaN/AlGaN exhibiting alarger band gap than InGaN, a current blocking layer, consisting ofAlBGaN or AlGaN having a large Al composition, exhibiting a smallerlattice constant must be formed, leading to remarkable differencebetween the lattice constants of the current blocking layer and a GaNlayer or a GaN substrate. Also in this case, effects similar to those ofthe aforementioned first to fourth embodiments can be attained byforming the current blocking layer only in the vicinity of a currentpath portion or reducing the thickness of the current blocking layer ina portion not in the vicinity of the current path portion. In this case,further, effects similar to those of the aforementioned fifth toeleventh embodiments can be attained by forming a semiconductor blockinglayer on a dielectric blocking layer.

While AlGaN is employed as the material for the n-type first and secondcladding layers in each of the aforementioned first to eleventhembodiments, the present invention is not restricted to this but then-type first and second cladding layers may be prepared from a materialsuch as AlGaN, AlBN or AlBINGaN having a different lattice constant fromthe underlayer.

While the n-type layers are formed followed by formation of the p-typelayers in each of the aforementioned first to eleventh embodiments, thepresent invention is not restricted to this but p-type layers mayalternatively be first formed on a substrate followed by formation ofn-type layers.

In each of the aforementioned first to eleventh embodiments, each of thenitride-based semiconductors may have either a wurtzite structure or azinc blende crystal structure.

While each nitride-based semiconductor layer is crystal-grown by MOVPEor the like in each of the aforementioned first to eleventh embodiments,the present invention is not restricted to this but crystal growth mayalternatively be performed by HVPE (halide or hydride VPE) or gas sourceMBE (molecular beam epitaxy) employing TMAl, TMGa, TMIn, NH₃, SiH₄ orCp₂Mg as material gas.

In each of the aforementioned second and third embodiments, the Alcomposition of Al_(x)Ga_(1-x)N forming the current blocking layer is setlarger than the Al composition of Al_(z)Ga_(1-z)N forming the n-typecladding layer closer to the substrate in relation to the emissionlayer. While cracks or lattice defects are easily caused when thecurrent blocking layer has a large Al composition, the present inventioncan inhibit the current blocking layer from formation of cracks orlattice defects. Consequently, the difference between the latticeconstants of the n-type cladding layer and the current blocking layercan be increased, thereby stabilizing transverse light confinement. Alsowhen the value x is less than or equal to the value z (x≦z), the currentblocking layer can be inhibited from formation of cracks or latticedefects according to the present invention. Thus, a similar effect canbe attained in the point that a current blocking layer having excellentcrystallinity can be formed.

While SiN is employed as the material for the dielectric blocking layerin each of the aforementioned fifth to eleventh embodiments, the presentinvention is not restricted to this but another nitride such as ZrN orTiN or an oxide such as SiO₂, ZrO₂ or TiO₂ may alternatively beemployed. The dielectric blocking layer is preferably prepared from amaterial having a smaller refractive index than the material for thecladding layer forming the current path portion. Further, the dielectricblocking layer is preferably prepared from a material absorbing lightgenerated from an active layer.

While the dielectric blocking layer is formed to have the thickness ofabout 50 nm in each of the aforementioned fifth to eleventh embodiments,the present invention is not restricted to this but the dielectricblocking layer may alternatively be formed to have a thickness withinabout 250 nm. When the dielectric blocking layer is formed to have athickness of about 250 nm, for example, the temperature characteristicof the nitride-based semiconductor laser device is slightly reduced dueto the increased thickness, thereby slightly increasing operatingcurrent under a high temperature.

While the semiconductor blocking layer 151 is grown to have the openingfor forming the current path portion in the aforementioned eighthembodiment, the present invention is not restricted to this but thesemiconductor blocking layer 151 may alternatively be temporarily formedon a region for forming the current path portion on the upper surface ofthe p-type first cladding layer 130 for thereafter removing the portionof the semiconductor blocking layer 151 for forming the current pathportion by RIE or the like.

While each nitride-based semiconductor layer is stacked on the (0001)plane of the nitride-based semiconductor in each of the aforementionedfirst to eleventh embodiments, the present invention is not restrictedto this but each nitride-based semiconductor layer may alternatively bestacked in another crystal orientation of the nitride-basedsemiconductor. For example, each nitride-based semiconductor layer mayalternatively be stacked on the (H, K, —H—K, 0) plane such as the(1-100) plane or the(11-20) plane of the nitride-based semiconductor. Inthis case, no piezoelectric field is formed on the emission layer andhence the radiation efficiency of the emission layer can be improved.

While the step portions 100 are so formed that the portions forming thecurrent path portion protrude and the side surfaces are substantiallyperpendicular to the substrate surface in the aforementioned secondembodiment, the shape of the step portions employable in the presentinvention is not restricted to this. For example, side surfaces of suchstep portions may have an oblique angle with respect to the substrate.In this case, an angle formed by the normal directions of the sidesurfaces of the step portions and the substrate surface may be less thanor greater than 90°. Further, the step portions may be so formed thatportions forming the current path portion are recessed. Further, eachstep portion may be formed by a plurality of steps.

1. A nitride-based semiconductor light-emitting device comprising: anemission later; a cladding layer, formed on said emission layer,including a first nitride-based semiconductor layer and having a ridgeportion; and a semiconductor current-blocking layer including a secondnitride-based semiconductor layer, wherein said ridge portion serves asa current path portion, and said semiconductor current-blocking layer isformed to cover the side surfaces of said current path portion such thatregions remote from said current path portion have no semiconductorcurrent-blocking layers.
 2. The nitride-based semiconductorlight-emitting device according to claim 1, wherein the total width ofsaid current path portion and said current blocking layer is at leastthree times and not more than seven times the width of said current pathportion.
 3. The nitride-based semiconductor light-emitting deviceaccording to claim 1, further comprising a mask layer, serving forselectively growing said current blocking layer, formed on portions ofthe upper surface of the first nitride-based semiconductor layer onwhich the current blocking layer is not formed.
 4. The nitride-basedsemiconductor light-emitting device according to claim 3, wherein saidmask layer is formed at a space of at least once and not more than threetimes the width of said current path portion from said current pathportion.
 5. The nitride-based semiconductor light-emitting deviceaccording to claim 3, wherein said mask layer includes an oxide film ora nitride film containing at least one element selected from a groupconsisting of Si, Ti and Zr.
 6. The nitride-based semiconductorlight-emitting device according to claim 1, wherein said cladding layerincludes a projection portion forming said ridge portion and a flatportion, and said current blocking layer is formed on the side surfacesof said projection portion and on said flat portion.
 7. Thenitride-based semiconductor light-emitting device according to claim 6,wherein said mask layer is formed on said flat portion of said claddinglayer, and said current blocking layer is formed on the side surfaces ofsaid projection portion of said cladding layer, on said flat portion ofsaid cladding layer and on said mask layer.
 8. The nitride-basedsemiconductor light-emitting device according to claim 1, wherein saidcurrent blocking layer includes an opening, and said cladding layerincludes: a first cladding layer having a substantially flat uppersurface, and a second cladding layer, formed on said first claddinglayer in said opening, having said current path portion.
 9. Thenitride-based semiconductor light-emitting device according to claim 1,wherein said current blocking layer contains at least one element,selected from a group consisting of B, Ga, Al, In and Tl, and N.
 10. Thenitride-based semiconductor light-emitting device according to claim 1,wherein said current blocking layer is formed either on a GaN substrateor on a GaN layer formed on a substrate, and includes said secondnitride-based semiconductor layer having a smaller lattice constant thanGaN.
 11. The nitride-based semiconductor light-emitting device accordingto claim 10, wherein said current blocking layer includes an Al GaNlayer.
 12. The nitride-based semiconductor light-emitting deviceaccording to claim 1, wherein said current blocking layer includes saidsecond nitride-based semiconductor layer having a refractive indexsmaller than the refractive index of said first nitride-basedsemiconductor layer forming said cladding layer.
 13. The nitride-basedsemiconductor light-emitting device according to claim 1, wherein saidcurrent blocking layer includes said second nitride-based semiconductorlayer having a lattice constant smaller than the lattice constant ofsaid first nitride-based semiconductor layer forming said claddinglayer.
 14. The nitride-based semiconductor light-emitting deviceaccording to claim 1, wherein said current blocking layer includes anAl_(w)Ga_(1-w)N layer, said cladding layer includes an Al_(v)Ga_(1-v)Nlayer, and said current blocking layer and said cladding layer areformed to have compositions satisfying w>v.
 15. The nitride-basedsemiconductor light-emitting device according to claim 1, wherein saidcurrent blocking layer is formed either on a GaN substrate or on a GaNlayer formed on a substrate, and includes said second nitride-basedsemiconductor layer having a lattice constant larger than the latticeconstant of GaN.
 16. The nitride-based semiconductor light-emittingdevice according to claim 15, wherein said current blocking layercontains InGaN.
 17. The nitride-based semiconductor light-emittingdevice according to claim 1, wherein said current blocking layerincludes said second nitride-based semiconductor layer absorbing lightemitted from said emission layer.
 18. The nitride-based semiconductorlight-emitting device according to claim 1, wherein said currentblocking layer includes an In_(s)Ga_(1-s)N layer, said emission layerincludes an In_(x)Ga_(1-x)N layer, and said current blocking layer andsaid emission layer are formed to have compositions satisfying s≧x. 19.A nitride-based semiconductor light-emitting device comprising: anemission layer; a cladding layer, fonned on said emission layer,including a first nitride-based semiconductor layer and having a ridgeportion; and a semiconductor current-blocking layer including a secondnitride-based semiconductor layer, wherein said ridge portion serves asa current path portion, and said semiconductor current-blocking layer isformed to cover the side surfaces of said current path portion such thata portion of said semiconductor current-blocking layer spaced apart fromsaid current path portion has a first thickness smaller than thethickness of a portion of the semiconductor current-blocking layer onsaid side surfaces of said current path portion.
 20. The nitride-basedsemiconductor light-emitting device according to claim 19, furthercomprising a step portion formed on a region spaced apart from saidcurrent path portion, wherein said portion of said current blockinglayer having said first thickness is formed on said step portion. 21.The nitride-based semiconductor light-emitting device according to claim20, wherein said step portion is spaced apart from said current pathportion by at least once and not more than three times the width of saidcurrent path portion.
 22. The nitride-based semiconductor light-emittingdevice according to claim 19, wherein said current blocking layercontains at least one element, selected from a group consisting of B,Ga, Al, Ia and Tl, and N.
 23. The nitride-based semiconductorlight-emitting device according to claim 19, wherein said currentblocking layer is formed either on a GaN substrate or on a GaN layerformed on a substrate, and includes said second nitride-basedsemiconductor layer having a smaller lattice constant than GaN.
 24. Thenitride-based semiconductor light-emitting device according to claim 23,wherein said current blocking layer includes an AlGaN layer.
 25. Thenitride-based semiconductor light-emitting device according to claim 19,wherein said current blocking layer includes said second nitride-basedsemiconductor layer having a refractive index smaller than therefractive index of said first nitride-based semiconductor layer formingsaid cladding layer.
 26. The nitride-based semiconductor light-emittingdevice according to claim 19, wherein said current blocking layerincludes said second nitride-based semiconductor layer having a latticeconstant smaller than the lattice constant of said first nitride-basedsemiconductor layer forming said cladding layer.
 27. The nitride-basedsemiconductor light-emitting device according to claim 19, wherein saidcurrent blocking layer includes an Al_(w)Ga_(1-w)N layer, said claddinglayer includes an Al_(v)Ga_(1-v)N layer, and said current blocking layerand said cladding layer are formed to have compositions satisfying w>v.28. The nitride-based semiconductor light-emitting device according toclaim 19, wherein said current blocking layer is formed either on a GaNsubstrate or on a GaN layer formed on a substrate, and includes saidsecond nitride-based semiconductor layer having a lattice constantlarger than the lattice constant of GaN.
 29. The nitride-basedsemiconductor light-emitting device according to claim 28, wherein saidcurrent blocking layer contains InGaN.
 30. The nitride-basedsemiconductor light-emitting device according to claim 19, wherein saidcurrent blocking layer includes said second nitride-based semiconductorlayer absorbing light emitted from said emission layer.
 31. Thenitride-based semiconductor light-emitting device according to claim 19,wherein said current blocking layer includes an In_(s)Ga_(1-s)N layer,said emission layer includes an In_(x)Ga_(1-x)N layer, and said currentblocking layer and said emission layer are formed to have compositionssatisfying s≧x.
 32. A nitride-based semiconductor light-emitting devicecomprising: an emission layer; a cladding layer, formed on said emissionlayer, including a laterally extending flat portion and a ridge portionhaving side surfaces extending from the flat portion; and acurrent-blocking layer, wherein said ridge portion serves as a currentpath portion, and said current-blocking layer is formed to cover theside surfaces of said current path portion, and said current-blockinglayer includes a dielectric blocking layer and a semiconductor blockinglayer formed on said dielectric blocking layer.
 33. The nitride-basedsemiconductor light-emitting device according to claim 32, wherein saiddielectric blocking layer includes an opening reaching the upper surfaceof said cladding layer, and said semiconductor blocking layer is incontact with the upper surface of said cladding layer through saidopening of said dielectric blocking layer.
 34. The nitride-basedsemiconductor light-emitting device according to claim 33, wherein saidsemiconductor blocking layer is formed by selective growth from theupper surface of said cladding layer located in said opening of saiddielectric blocking layer.
 35. The nitride-based semiconductorlight-emitting device according to claim 32, wherein the thickness ofsaid dielectric blocking layer is smaller than the thickness of saidsemiconductor blocking layer.
 36. The nitride-based semiconductorlight-emitting device according to claim 32, wherein said currentblocking layer is formed on the side surfaces of said projection portionand on said flat portion.
 37. The nitride-based semiconductorlight-emitting device according to claim 36, wherein said dielectricblocking layer is formed on said flat portion of said cladding layer,and said semiconductor blocking layer is formed on the side surfaces ofsaid projection portion of said cladding layer and on said dielectricblocking layer formed on said flat portion.
 38. The nitride-basedsemiconductor light-emitting device according to claim 37, wherein saidsemiconductor blocking layer is formed by selective growth from the sidesurfaces of said projection portion of said cladding layer.
 39. Thenitride-based semiconductor light-emitting device according to claim 32,wherein said current blocking layer includes an opening, and saidcladding layer includes: a first cladding layer having a substantiallyflat upper surface, and a second cladding layer, formed on said firstcladding layer in said opening of said current blocking layer, havingsaid current path portion.
 40. The nitride-based semiconductorlight-emitting device according to claim 39, wherein said secondcladding layer is formed to extend onto the upper surface of saidcurrent blocking layer.
 41. The nitride-based semiconductorlight-emitting device according to claim 32, wherein a number ofvertical dislocations is reduced in said semiconductor blocking layerdue to transversely bent dislocations.
 42. The nitride-basedsemiconductor light-emitting device according to claim 32, wherein saidsemiconductor blocking layer is formed only in the vicinity of saidcurrent path portion.
 43. The nitride-based semiconductor light-emittingdevice according to claim 32, wherein said semiconductor blocking layercontains at least one element, selected from a group consisting of B,Ga, Al, In and Tl, and N.
 44. The nitride-based semiconductorlight-emitting device according to claim 32, wherein said cladding layerincludes a first nitride-based semiconductor layer, and saidsemiconductor blocking layer is formed either on a GaN substrate or on aGaN layer formed on a substrate, and includes a second nitride-basedsemiconductor layer having a smaller lattice constant than GaN.
 45. Thenitride-based semiconductor light-emitting device according to claim 44,wherein said semiconductor blocking layer includes an AlGaN layer. 46.The nitride-based semiconductor light-emitting device according to claim32, wherein said cladding layer includes a first nitride-basedsemiconductor layer, and said semiconductor blocking layer includes asecond nitride-based semiconductor layer having a refractive indexsmaller than the refractive index of said first nitride-basedsemiconductor layer forming said cladding layer.
 47. The nitride-basedsemiconductor light-emitting device according to claim 32, wherein saidcladding layer includes a first nitride-based semiconductor layer, andsaid semiconductor blocking layer includes a second nitride-basedsemiconductor layer having a lattice constant smaller than the latticeconstant of said first nitride-based semiconductor layer forming saidcladding layer.
 48. The nitride-based semiconductor light-emittingdevice according to claim 32, wherein said current blocking layerincludes an Al_(w)Ga_(1-w)N layer, said cladding layer includes anAl_(v)Ga_(1-v)N layer, and said current blocking layer and said claddinglayer are formed to have compositions satisfying w>v.
 49. Thenitride-based semiconductor light-emitting device according to claim 32,wherein said cladding layer includes a first nitride-based semiconductorlayer, and said semiconductor blocking layer is formed either on a GaNsubstrate or on a GaN layer formed on a substrate, and includes a secondnitride-based semiconductor layer having a lattice constant larger thanthe lattice constant of GaN.
 50. The nitride-based semiconductorlight-emitting device according to claim 49, wherein said semiconductorblocking layer contains InGaN.
 51. The nitride-based semiconductorlight-emitting device according to claim 32, wherein said cladding layerincludes a first nitride-based semiconductor layer, and saidsemiconductor blocking layer includes a second nitride-basedsemiconductor layer absorbing light emitted from said emission layer.52. The nitride-based semiconductor light-emitting device according toclaim 32, wherein said semiconductor blocking layer includes anIn_(s)Ga_(1-s)N layer, said emission layer includes an In_(x)Ga_(1-x)Nlayer, and said semiconductor blocking layer and said emission layer areformed to have compositions satisfying s≧x.
 53. The nitride-basedsemiconductor light-emitting device according to claim 32, wherein saiddielectric blocking layer includes an oxide film or a nitride filmcontaining at least one element selected from a group consisting of Si,Ti and Zr.
 54. The nitride-based semiconductor light-emitting deviceaccording to claim 53, wherein said dielectric blocking layer includesan SiN film.
 55. A nitride-based semiconductor light-emitting devicecomprising: an emission layer; a cladding layer, formed on said emissionlayer, including a first nitride-based semiconductor layer; and asemiconductor current-blocking layer including a second nitride-basedsemiconductor layer and having an opening, wherein said opening servesas a current path portion, and said semiconductor current-blocking layeris formed on portions of said emission layer but not on other portionsof said emission layer remote from said current path portion.
 56. Anitride-based semiconductor light-emitting device comprising: anemission layer; a cladding layer, formed on said emission layer; and acurrent-blocking layer having an opening, wherein said opening serves asa current path portion, and said current-blocking layer includes adielectric blocking layer formed on and in direct contact with saidcladding layer, and a nitride-based semiconductor blocking layer formedon said dielectric blocking layer, wherein said nitride-basedsemiconductor blocking layer absorbs light emitted from said emissionlayer.